Materials & Finishing

Period-correct steel grades; parkerized, oil-blacked, suncorite-painted; modern equivalents

(Generated by build/inject_toc.py at build time. Section headers below are the source of truth.)

Materials and surface treatments used in the original WWII Stens, the modern equivalents a Path B or Path C builder would substitute, and the procedure for applying each finish are documented here. This volume is the load-bearing reference for Vol 6 § 6.8 (parts-kit finishing) and Vol 7 § 7.3 + § 7.8 (from-scratch materials selection and finishing).

Three guiding facts shape the materials-and-finishing posture for a Sten:

The 1941 design specified the cheapest available wartime materials. The Sten was deliberately engineered for crude wartime production with low-carbon mild steel, minimal heat treatment, and inexpensive surface finishes (parkerizing, suncorite paint, sometimes just oil-blacking). A modern builder can use better materials — and probably should for the bolt and chamber-bearing parts — but the receiver tube does not need to be heat-treated alloy steel; mild steel is the original specification and is fully adequate at 9×19 pressure.
Per-factory finish variation was substantial. RSAF Enfield, BSA, Fazakerley, Long Branch, Lithgow, and the smaller subcontracted shops each had their own finishing-line practices. There is no single “correct Sten finish” — match a specific Mk and factory if period accuracy is the goal, or pick a representative finish for the build’s aesthetic.
The wartime finishes were workshop-grade. They were not heavily preserved, were not “collector quality,” and showed wear quickly. Modern parkerizing using current solutions produces a finish better than most WWII Stens left the factory with. This is fine for a build — the historically-correct finish is “rough.”

The volume is organized in three parts: § 9.2 through § 9.6 cover the metal finishes (parkerizing as canonical, hot blue and Cerakote as alternatives, plus heat-treat and case-hardening); § 9.7 covers the wood finishes for Mk V furniture; § 9.8 covers periodic-maintenance refinishing.

9.1 Period-correct materials by part

The WWII material spec for each major component, cross-referenced from Vol 4:

Table 1 — The WWII material spec for each major component, cross-referenced from [Vol 4](vol4.md)

Part	WWII spec	Modern equivalent	Notes
Receiver tube	Cold-rolled mild steel sheet, ~1.5 mm wall, no heat treatment	1018 cold-rolled sheet, 0.060″ / 1.5 mm. A36 hot-rolled acceptable but less smooth.	Mild steel; weldable; no need for alloy steel at 9×19 chamber pressure.
Bolt	Plain carbon steel, ~32 mm OD; bolt face case-hardened to ~Rc 50	4140 alloy steel preferred; case-hardened bolt face to Rc 55–58, body remains at ~Rc 28–30 base. 1045 carbon steel acceptable as alternative.	Case-hardening on the bolt face is required; the rest of the bolt is intentionally tough but not brittle.
FCG housing (Mk II UK)	Stamped sheet mild steel, 16-gauge, welded	16-gauge 1018 sheet or 6061-T6 aluminum for CNC-machined version (Vol 4 § 4.5; Vol 7 § 7.5).	Stamped sheet is period-correct; CNC-machined aluminum is cleaner and faster for a one-off build.
FCG housing (Long Branch Mk II)	Cast aluminum (typically 4xx-series casting alloy)	6061-T6 aluminum bar stock for CNC-machined version.	The cast Long Branch housing is a specific period-correct variant; CNC-machined from bar stock is the cleaner modern path.
FCG internal parts (trigger, sear, disconnector, magazine catch)	Stamped or machined steel, often 1018 or similar mild carbon; sear engagement case-hardened	4140 alloy steel for new builds; sear engagement case-hardened to Rc 50–55.	Hardness on the engagement surfaces is critical; the part bodies don’t need to be hard.
Barrel	Mild steel, button-rifled or cut-rifled in 9×19, ~197 mm length	4150 chrome-moly (canonical modern barrel-blank material) or 416R stainless (corrosion-resistant alternative).	Pre-rifled barrel blanks from US barrel-blank vendors (E.R. Shaw, Green Mountain, McGowen, McCory, Bear Creek).
Recoil spring	Music wire, hand-wound	ASTM A228 music wire, ~280 mm free length, ~8 mm coil OD	Aftermarket springs available from Bear Arms and similar.
FCG springs	Music wire, hand-wound	ASTM A228 music wire, per Vol 4 § 4.5 dimensional spec	New build: wind on a mandrel to the Vol 4 spec.
Stock (Mk II skeleton T)	Mild steel rod, ~9.5 mm OD, welded T-shape	1018 round bar, 9.5 mm OD, bent and welded	Simple fabrication; bend at the joint, TIG-weld.
Stock (Mk V buttstock)	Walnut hardwood, finished with linseed oil	American walnut, birch, or beech	Mk V stocks vary in wood species by production batch; walnut is most-common.
Foregrip (Mk V)	Walnut hardwood	Same as stock.
Magazine body	Stamped sheet mild steel	1018 sheet, 0.030″ / 0.75 mm for fabricated; commercial aftermarket for builders not making magazines	Sterling-pattern aftermarket magazines (Bear Arms, ASP) are the canonical modern recommendation.
Muzzle bushing, rear cap, miscellaneous small parts	Mild steel, machined	1045 carbon steel or 4140	Machined-on-lathe parts; no special heat treatment unless threading wear is a concern.

9.2 Parkerizing — the canonical finish

Parkerizing (chemical phosphate conversion coating) was the standard military finish for WWII US and UK small arms, including most Sten production. It produces a porous matte-gray surface that holds oil and resists corrosion. Two phosphate chemistries dominate:

Manganese phosphate — dark gray, almost black; the canonical military finish; what most Sten production used.
Zinc phosphate — lighter gray; sometimes used for less-stressed components; common for postwar-production small arms in some countries.

For a Sten build, manganese phosphate is the period-correct finish. The procedure:

9.2.1 Surface preparation

The parkerizing reaction requires bare iron/steel as the substrate. All paint, plating, prior parkerizing, oil, and surface oxide must be removed:

Mechanical preparation — strip with media blasting (aluminum oxide, 80–120 grit) for fastest and most uniform surface; or wire-brush wheel on a bench grinder for less-uniform but adequate results. Avoid burnishing tools that smooth the surface — parkerizing needs micro-roughness to bond.
Chemical preparation — degrease in acetone, brake cleaner, or trichloroethylene (the last is restricted; use sparingly with adequate ventilation). Verify water-break-free surface — water should sheet across the cleaned part without beading.
Avoid skin contact with the cleaned part after preparation. Skin oils produce uneven parkerizing.

9.2.2 Solution preparation

Commercial manganese phosphate solution is sold in concentrate form by:

Du-Lite Corporation (one of the long-time US suppliers of military-grade phosphate solutions)
Lauer Custom Weaponry (gunsmith-market supplier; smaller batch sizes)
Brownells (re-packaged supplier; convenient for smaller shops)
Homebrew recipes (manganese dihydrogen phosphate + zinc nitrate + nitric acid in specific proportions; published in machinist references and forum archives — not recommended without a solid chemistry background).

Typical commercial concentrate dilutes to ~2–5% solution in distilled water. Use distilled or deionized water — tap water minerals contaminate the bath and produce uneven finishes.

9.2.3 Tank setup

Tank options for a 530 mm-long Sten receiver:

Stainless steel tank — ideal; doesn’t react with the solution. A 600 mm × 200 mm × 200 mm stainless tank holds about 24 L of solution; that’s enough for a Sten build with parts immersed in batches.
Glass tank (aquarium-style) — works for smaller batch sizes; verify the glass tolerates 95°C operating temperature.
Pyrex pan — works for small parts batch sizes; use multiple immersions for the full receiver.
Avoid steel tanks other than stainless — carbon-steel tanks will themselves react with the parkerizing solution.

Heat source: an immersion heater (1500 W in a stainless tank handles a 24-L bath at temperature) or a hot plate under the tank.

9.2.4 Procedure

Heat the solution to 95–100°C. Verify with a thermometer; the reaction rate is temperature-sensitive.
Pre-rinse the prepared part in clean hot water (90°C) for 30 seconds to bring the part up to temperature without thermal shock.
Immerse in the parkerizing bath, fully submerged. Suspend with stainless wire or stainless hooks — no steel wire that will itself react.
Initial reaction: vigorous bubbling for the first 1–3 minutes as the chemical reaction starts. This is normal.
Continue for 15–30 minutes total dwell time. The reaction slows as the phosphate coating reaches its limit thickness; further immersion adds little.
Verify visually — the part should be uniformly dark gray. Patches or streaks of bright steel indicate incomplete coverage (re-immerse) or surface contamination (re-strip and start over).
Rinse in clean hot water (90°C, distilled) immediately on removal.
Oil immediately while the part is still hot — the porous parkerized surface drinks oil while warm. CLP (Mil-Spec Cleaner-Lubricant-Preservative), Mobil 1 motor oil, Outers Gun Oil, or 3-in-1 oil all work. Apply liberally; wipe excess after 24 hours.
Cure for 24 hours before assembly or further handling. The parkerized surface continues to oxidize and stabilize during this period.

9.2.5 Color and uniformity control

The final color depends on:

Solution temperature (higher temperature → darker finish, within the 90–100°C operating range).
Dwell time (longer time → darker, up to the coating thickness limit).
Solution concentration (higher concentration → darker).
Surface preparation (more thoroughly blasted → more uniform).
Base material (1018 mild steel produces a slightly different color than 4140 alloy; aluminum FCG housings parkerize differently from steel housings and may need a separate finishing process — typically anodizing for aluminum).

For matching multiple parts in a build, process them together in the same bath at the same time. Sequential processing produces visibly different color batches that don’t match well.

9.2.6 Aluminum parts (Long Branch Mk II or Vol 7 CNC-machined FCG)

Aluminum doesn’t parkerize the same way steel does. For aluminum FCG housings or other aluminum parts:

Anodize — type II clear anodize or type III hard anodize, gray/black dye. Send out to a commercial anodizer (cost ~$30–80 for a FCG-housing-sized part). Produces a darker, harder finish than parkerized steel; visually matches reasonably well from conversational distance.
Cerakote — alternative; matches the gray of parkerized steel reasonably well when the color is specified. See § 9.4.
DuraCoat or KG Gun Kote — older alternatives to Cerakote; functionally similar.

9.3 Hot blue — the alternative finish

Hot blue (caustic-blue) was less common than parkerizing for Sten production but appears on some refinished post-war specimens. It’s a black oxide conversion produced by immersion in a hot sodium-hydroxide-and-nitrate solution at ~140°C. The result is a smooth black or near-black surface — visually different from parkerized (smoother, glossier) and not period-correct for a wartime Sten, but acceptable for a modern build that prioritizes appearance over historical authenticity.

The procedure:

Surface preparation — same as parkerizing (media-blasted bare steel).
Pre-clean in alkaline cleaner to ensure no contamination.
Immerse in hot blue bath (commercial bluing salts, dissolved in water at ~140°C) for 10–20 minutes.
Rinse in hot water.
Water displacement — dip in water-displacement solution (commercial gun-bluing post-immersion oil; or for homebrew, soluble oil) to push water out of the porous oxide layer.
Oil and cure for 24 hours.

Hot blue is less corrosion-resistant than parkerizing because the oxide layer is thinner and smoother (less surface area for oil retention). Maintenance is more frequent — wipe with oil after every range session.

Caustic blue at 140°C is dangerous. The bath is corrosive; splashes burn skin instantly. The fumes are caustic. PPE (face shield, rubber apron, gloves) is non-negotiable. Many Sten builders skip hot blue for safety reasons and go straight to parkerizing or Cerakote.

9.4 Cerakote — the modern non-period-correct alternative

Cerakote (and competitors DuraCoat, KG Gun Kote, GunKote) is a ceramic-polymer firearm finish applied by spray and cured at 150–250°C in a domestic oven. It’s not period-correct — Cerakote didn’t exist until the 1980s — but it’s dramatically more durable than parkerizing or hot blue, and the color match to “matte black” or “matte gray” is good enough that a Cerakoted Sten looks plausibly period-correct from conversational distance.

Cerakote pros:

Hardness ~Mohs 7 (vs ~Mohs 3 for parkerizing) — resistant to scratches and wear.
Strong corrosion resistance; salt-fog rating typically 500+ hours (vs ~100 hours for parkerizing).
Many color options; matte black, matte gray, and various tactical-style colors available.
Self-color-matching by the manufacturer.

Cerakote cons:

Not period-correct.
Requires a spray gun (HVLP airbrush or compressor + spray gun).
Requires a cure oven (a dedicated household oven or a temperature-controlled cabinet — not a food-use kitchen oven).
More expensive than parkerizing (~$30–80 for the supplies vs $15–30 for parkerizing).

The procedure (abbreviated; detailed Cerakote-specific procedures are published by NIC Industries, the Cerakote manufacturer):

Surface preparation — media-blasted bare steel; same as parkerizing.
Degrease and dry thoroughly.
Mix the Cerakote per manufacturer’s spec; typically a 2-part liquid that activates 15–30 minutes before spray.
Spray-apply to a thin even coat (~0.001″–0.002″ per coat); apply 1–2 coats for the body color.
Cure at 150°C (or per the specific Cerakote variant; some are room-temperature-cure) for 1–2 hours.
Cool and assemble.

Cerakote is a one-and-done finish; periodic maintenance is limited to wiping with a damp cloth.

9.5 Heat treatment and case hardening

The Sten’s wartime spec was minimal heat-treatment: mild steel parts with case-hardened sear engagement and bolt face, nothing else. A modern build follows the same principle but with better surface-hardening control.

9.5.1 Bolt face

The bolt face contacts the case head at firing-pressure (~36,500 psi); without case-hardening, the bolt face gradually deforms under repeated firing. The wartime spec called for case-hardened steel; modern equivalents:

Pack carburizing — pack the bolt face in a steel can with Casenit or Cherry Red Compound carburizing material, heat to ~900°C for 60–90 minutes, then quench in water or oil. Produces case depth ~0.5–1.0 mm at Rc 55–58. Body remains at base hardness (~Rc 28–30 for 4140).
Salt-bath carburizing — gunsmith specialty; uses a molten salt bath to carburize. Produces deeper, more-uniform case. Commercial-shop process; cost ~$50–100 for a Sten bolt.
Induction hardening — for shops with an induction heater. Faster and more localized than pack carburizing.

The bolt face hardness target is Rc 55–58 over 0.5–1.0 mm depth. Verify with a hardness tester (Rockwell C scale) or a hardness file set.

9.5.2 FCG sear engagement

The sear engagement surfaces (where the sear contacts the bolt’s sear surface, and the trigger contacts the sear, in either open-bolt or closed-bolt designs) need to be case-hardened for durability. The wartime spec was Rc 50–55 on the engagement surfaces; modern equivalents:

Local case hardening with Kasenit — coat the engagement surface with Kasenit (a carbonizing flux), heat with a torch to ~900°C, quench. Local; doesn’t affect surrounding part geometry. Produces case depth ~0.3–0.5 mm at Rc 50–55.
Pack carburizing — same as bolt-face procedure; works for separate FCG parts.

9.5.3 Receiver tube

The receiver tube does not need heat treatment. Mild steel (1018 cold-rolled) is the WWII spec and is adequate. The 9×19 chamber pressure of 36,500 psi is below the yield strength of cold-rolled 1018 (~50,000 psi yield), with substantial design margin. Avoid heat-treating the receiver tube — it would warp the wrapped-and-welded geometry and may crack at the weld seam.

9.5.4 Barrel

A purchased pre-rifled barrel blank (Vol 7 § 7.7 Step D1) arrives heat-treated by the manufacturer. Do not re-heat-treat — manufacturer specifications are already optimized for the barrel-blank steel (typically 4150 chrome-moly normalized for stress-relief).

The chamber-cut operation (Vol 7 § 7.7 Step D3) does not require post-cut heat treatment for a 9×19 pistol-pressure barrel. Wipe with cutting oil, clean, and verify with bore mirror.

9.5.5 Welded receiver-tube stress relief

The longitudinal weld on the receiver tube (Vol 7 § 7.4 Step A5) can introduce residual stress that, under thermal cycling from sustained fire, could lead to crack propagation. A sub-critical anneal at ~620°C for 30 minutes after welding relieves this stress without changing the mild-steel base hardness.

If lab capability supports the anneal (a kiln or oxyacetylene torch with controlled heat), perform it. If not, the as-welded receiver is probably fine at 9×19 pressure but is more-conservative without the relief step.

9.6 Weld preparation for the receiver-tube seam

The receiver-tube longitudinal weld is the only structural weld in a from-scratch Sten build. Vol 7 § 7.3.3 covers the welding procedure; Vol 9 covers the finishing-side details.

Pre-weld surface prep:

Joint edges: ground perpendicular to the sheet face; ±0.2 mm joint gap when clamped on mandrel.
Surfaces adjacent to the weld: clean to bare steel; remove mill scale, oil, paint, surface oxide.
No anti-spatter compound on the joint — anti-spatter can contaminate the weld pool.

Post-weld finishing:

Grind the weld bead flush with the receiver-tube OD on the outside surface, using a flap wheel or hand grinder. The inside surface of the receiver tube was supported by a copper backing strip during welding (Vol 7 § 7.3.3) and the bead inside should be flat or slightly concave — no grinding needed.
Verify the weld: visually inspect for porosity, cracks, or undercut. A dye-penetrant test (Spotcheck or similar) reveals subsurface defects.
Stress-relieve if lab capability supports it (§ 9.5.5).
Inspect again before finishing.

A correctly-prepared weld is invisible after parkerizing or Cerakote — the seam is dressed flush, the surface is uniform, and the finish covers the slight grain difference. A poorly-prepared weld shows through any finish as a visible discontinuity.

9.7 Wood finishes for Mk V furniture

The Mk V Sten has a wooden buttstock and foregrip (Vol 3 § 3.5). The wartime UK production used walnut with a boiled linseed oil finish — period-correct, slow to build, and produces the satin sheen that’s iconic on British military furniture (Lee-Enfield, Sterling, etc.).

9.7.1 Wood selection

For a Mk V buttstock or foregrip:

American black walnut (Juglans nigra) — most-period-correct; common in commercial gunstock blanks (Boyds, Macon Gunstocks).
English walnut (Juglans regia) — period-correct but more expensive.
European beech — alternative; less figured but acceptable.
Birch — alternative; less period-correct but more affordable.

Source a blank from a commercial gunstock supplier or shape from solid hardwood. CNC-router workflow (cross-ref Vol 7 § 7.12.1 for the Mk V conversion) can rough-shape the blank from a 50 mm × 200 mm × 400 mm hardwood block.

9.7.2 Surface preparation

After CNC-routing or hand-shaping:

Sand progressively — 80 grit → 120 grit → 180 grit → 220 grit → 320 grit. Each pass removes the scratches from the previous grit.
Final dry sanding at 320 grit produces a smooth surface.
Wet down with water to raise the grain, then re-sand at 320 grit to knock the raised grain down. Repeat 2–3 times until the grain stays down after wetting.
Final sand at 400 grit if a glassy finish is desired; 320 grit for a more-period-correct semi-matte finish.

9.7.3 Boiled linseed oil finish (period-correct)

The canonical Mk V furniture finish. Boiled linseed oil (BLO) is linseed oil with metal-salt driers added to accelerate the curing process. The finish:

Apply BLO liberally by hand or with a clean cloth. Saturate the wood surface.
Wait 15–30 minutes for the oil to soak in.
Wipe off excess with a clean cloth.
Cure for 24 hours in a warm, well-ventilated space (BLO-soaked rags can spontaneously combust — dispose in a metal can with water).
Repeat steps 1–4 for 5–10 cycles. The finish builds gradually; early coats soak in, later coats build a thin film.
Periodic refresh — every 1–2 years, apply a single BLO coat to maintain the finish.

The result is a deep satin sheen with the wood grain visible and accentuated. Period-correct for the Mk V.

9.7.4 Alternative wood finishes

Tru-Oil (Birchwood Casey) — modern oil-and-resin finish that builds faster than BLO and produces a slightly glossier surface. Not period-correct but common in modern gunsmith work. Apply per Tru-Oil instructions; 3–5 coats typical.
Tung oil — natural alternative to BLO; slightly different curing chemistry; produces a similar period-correct satin finish.
Polyurethane — modern wood finish; durable but produces a plastic-looking surface that doesn’t match WWII wartime production. Not recommended for a Mk V build.

9.8 Periodic-maintenance refinishing

Parkerized and Cerakoted finishes will eventually wear — at edges, at high-contact surfaces, and where the gun rubs against carrying gear. Refinishing schedule:

9.8.1 Parkerized finish

Annual touch-up — apply a thin coat of CLP or 3-in-1 oil to the entire metal surface after annual cleaning (Vol 11 § 11.7.2). The parkerized surface drinks the oil and refreshes its appearance.
Spot refinish every 3–5 years — for wear spots, strip back to bare metal locally, brush-blast or hand-sand, and re-parkerize the local area. Color-match by adjusting solution temperature and dwell time against the surrounding finish (cross-ref § 9.2.5).
Complete strip-and-reparkerize every 10+ years — if the entire gun’s finish is degraded, strip all metal parts, re-blast, re-parkerize in a single batch.

9.8.2 Cerakote finish

Minimal maintenance — Cerakote is harder than parkerizing and resists wear for years.
Wipe with damp cloth as needed; no oil required.
Spot refinish for damage — strip locally, mask the surrounding area, respray and cure.

9.8.3 Wood finish

Annual BLO coat for Mk V furniture — apply, wait, wipe per § 9.7.3.
Repair scratches and dents — for deep scratches, sand back to clean wood, build up with BLO; for dents, steam-raise with a wet cloth and hot iron, then re-sand and re-finish.

9.9 Color and aesthetic choices

A Sten build can target several aesthetic targets:

9.9.1 Fresh-1944 appearance

Uniform manganese-phosphate parkerizing in the standard dark-gray-to-near-black color, matched across all metal parts. Wood furniture (Mk V) in fresh BLO finish, walnut grain visible. This is the canonical “freshly issued in 1944” look — what a Sten looked like leaving the factory.

9.9.2 Weathered-veteran appearance

Original WWII-finish kit parts (retained from the parts kit), patinated by 80 years of use. New US receiver tube and replacement parts parkerized to a slightly-mismatched darker shade so the build looks like an old gun with replacement service parts. Wood furniture lightly distressed (sanded edges, occasional dings) and BLO-finished. This is the “build with the past” aesthetic.

9.9.3 Tactical / non-period

Cerakote in matte black, gray, or FDE/OD. Modern aftermarket rail-mounted optic, modern aftermarket magazines. Wood furniture replaced with modern synthetic. This is the “Sten chassis with modern dress” aesthetic — non-period but mechanically sound.

9.9.4 Collector-display

Mirror-blacked hot blue finish on all metal; high-figure walnut Mk V furniture finished with multiple BLO cycles; no carry wear. This is the “presentation gun” aesthetic — not for range use, displayed in a glass case. Uncommon for Sten builds (the gun’s design aesthetic is workshop-grade, not presentation-grade) but possible.

The hub’s canonical Vol 7 build targets option 1 (fresh-1944); Vol 6 Path B builders often choose option 2 (weathered-veteran) to preserve kit-part patina; option 3 (tactical) is supported but not the canonical hub aesthetic; option 4 (collector-display) is supported for builders who want it.

9.10 References (Vol 9)

Vol 4 of this series — Engineering & Reference Data; the dimensional source for parts and materials.
Vol 6 of this series — Build Path B; § 6.8 calls out this volume for the parts-kit finishing-or-preserve-patina decision.
Vol 7 of this series — Build Path C; § 7.3.3 (weld prep) and § 7.8 Step E8 (finishing) call out this volume.
Vol 11 of this series — Live-Fire Operation & Use; § 11.7.2 (deep cleaning) cross-references this volume for refinishing.
Du-Lite Corporation. Manganese Phosphate Solutions. (Commercial parkerizing supplier; technical data sheets available on the Du-Lite site.)
Lauer Custom Weaponry. DuraBake Parkerizing Solutions. (Gunsmith-market parkerizing supplier.)
Brownells. Bluing and Parkerizing Catalog. (Re-packaged parkerizing and bluing supplies.)
NIC Industries. Cerakote Application Guide. (The manufacturer’s procedure for Cerakote application and cure.)
Birchwood Casey. Sheath, Tru-Oil, Casey Bluing Catalog. (Long-term storage oil, wood finishes, hot blue solutions.)
Boyds Gunstock Industries, Macon Gunstocks. Commercial gunstock blank suppliers for Mk V furniture.
ASTM A228 — music wire specification for FCG springs and recoil springs.
AISI 1018 Cold-Rolled Mild Steel — canonical receiver-tube material.
AISI 4140 / 4150 Alloy Steel — canonical bolt and barrel material.
Machinery’s Handbook. General machinist reference for material specs, heat-treatment, and surface-finish procedures.
Skennerton, Ian. The Sten Machine Carbine. For period-correct finish identification and per-factory variation.
Iannamico, Frank. The STEN Submachine Gun. For per-Mk finish references and production-line details.