Imperial UNC brass threaded insert for plastics — engineering drawing (Brassland).
Specification
| Standard | Manufacturer-specific — no ANSI/ASME dimensional standard exists for inserts for plastics |
| Types | Tapered heat-set / ultrasonic inserts and straight-knurl press-in inserts; flanged variants on request |
| Thread | 2-56 to 3/8-16 UNC; UNF pairs (10-32, 1/4-28, 5/16-24, 3/8-24) per catalog series |
| Material | C36000 free-machining brass (UNS) — EN twin CW614N (CuZn39Pb3); lead-free C69300 / CW724R on request |
| Certificate | EN 10204 3.1 per shipment; 3.2 on request |
Range guide — imperial inserts for plastics
| Thread | Styles | Typical length range (in.) | Typical starting-hole series (in.) |
|---|---|---|---|
| 2-56 | Press-in · heat-set | 0.115 – 0.188 | ≈ 0.123 – 0.129 |
| 4-40 | Press-in · heat-set | 0.135 – 0.285 | ≈ 0.156 – 0.159 |
| 6-32 | Press-in · heat-set | 0.150 – 0.250 | ≈ 0.188 – 0.206 |
| 8-32 | Press-in · heat-set | 0.185 – 0.375 | ≈ 0.219 – 0.234 |
| 10-24 / 10-32 | Press-in · heat-set | 0.150 – 0.375 | ≈ 0.250 – 0.277 |
| 1/4-20 / 1/4-28 | Press-in · heat-set | 0.300 – 0.500 | ≈ 0.313 – 0.315 |
| 5/16-18 / 5/16-24 | Press-in · heat-set | 0.335 – 0.563 | ≈ 0.363 – 0.375 |
| 3/8-16 / 3/8-24 | Press-in · heat-set | 0.375 – 0.625 | ≈ 0.438 – 0.448 |
Ranges span two independently verified US catalog series (straight-knurl press-in and tapered heat-set, July 2026). Knurl OD and exact lengths are vendor-specific and NOT interchangeable between makes — installed hole size and boss diameter are always per the manufacturer drawing. Test-fit before production. Full dimension chart: UNC threaded insert dimension chart →
Per-drawing guidance
The hole-size series is broadly consistent across vendors — a 4-40 insert installs in a ≈0.156–0.159 in. hole, an 8-32 in ≈0.219–0.234 in., a 1/4-20 in ≈0.313–0.315 in. — but knurl geometry, flange diameters and length steps differ from catalog to catalog. Published design guides also recommend a minimum hole depth of insert length plus roughly 0.030 in. and a minimum boss diameter of about twice the knurl OD for heat-set styles. Send the insert drawing (or a competitor part number) and we will machine to it; if you are designing fresh, we supply the drawing for approval with the quotation.
Boss & hole design rules
Insert body OD and length are made to your drawing, but boss and hole geometry follow well-established design rules from established insert-design references. These apply to both heat-set and press-in styles.
| Boss outer Ø | 2–3× insert Ø (equivalently ≈2–2.5× hole Ø); multiplier shrinks as the insert grows |
| Min. hole depth | Insert length + 2 thread pitches (heat-set, press-in); ≥1.2× length for self-tapping |
| Flush install | Top flush, max +0.005″ (0.13 mm) proud; never sub-flush (jack-out risk) |
| Lead-in taper | Straight hole ≤1° included; tapered hole 8° included (with a tapered insert) |
| Filler correction | Open the hole ~0.003″ (0.08 mm) at 15%+ filler, ~0.006″ (0.15 mm) at 35%+; interpolate between |
| Headed counterbore | Ø = head Ø + 0.02–0.05″ (0.5–1.3 mm), depth = head thickness |
Oversize holes cut pull-out and torque; undersize holes crack the boss. Moulded holes out-perform drilled. Full method tables & heat-set temperatures: insert installation guide →
Indicative performance — pull-out & torque-out
| Thread | Pull-out unfilled (N) | Pull-out 30% GF (N) | Torque-out unfilled (Nm) | Torque-out 30% GF (Nm) |
|---|---|---|---|---|
| 4-40 | 650–1,650 | 700–1,500 | 1.5–3 | 3.7–4 |
| 6-32 | 1,000–2,900 | 1,300–2,300 | 2.5–6 | 4.5–6 |
| 8-32 | 1,350–3,700 | 1,600–3,900 | 4–10 | 7–10 |
| 10-24 / 10-32 | 1,700–4,600 | 2,900–3,900 | 5–16 | 14–20 |
| 1/4-20 | 2,800–8,200 | on request | 10–26 | on request |
Indicative typical performance only — correctly installed heat-set/ultrasonic inserts in representative engineering thermoplastics (unfilled nylon/ABS/PC and 30% glass-filled nylon), as a general design guide. Actual performance depends heavily on your resin and filler, hole and boss geometry, and installation process. Always validate on your own boss, resin and process; contact us for application-specific data. Figures are ranges, not spec numbers. Glass fill does not reliably raise pull-out — it mainly raises torque-out, stiffness and creep resistance. The 1/4-20 glass-filled figures rest on a single source and are supplied on request.
Heat-set vs press-in
Tapered heat-set / ultrasonic inserts are driven into thermoplastics with heat or ultrasonic energy that locally re-melts the boss so plastic flows into the knurls. Straight-knurl press-in inserts are pressed cold into a plain hole. Which style holds better depends on the plastic, boss design and pull-out/torque-out requirement — both are made to order here in brass. For metric mould-in styles see DIN 16903 moulding inserts; for self-tapping and barbed styles see special inserts.
Imperial & UNC range
Related pages
Expansion & knurled threaded inserts.
View →ProductSelf-tapping, barbed & press-in styles.
View →Metric equivalentMetric mould-in insert range.
View →ToolChoosing and installing inserts.
View →MaterialUS free-machining brass datasheet.
View →IndustryInserts for housings and enclosures.
View →Quote in 24 hours.
Give the standard, thread, finish and quantity. We machine inch-series brass parts in Jamnagar, India, and export to 40+ countries.
Sources & references
Length ranges and starting-hole series compiled from two independent published US insert-catalog series (one straight-knurl press-in line, one tapered heat-set line), cross-checked July 2026. Because insert geometry is proprietary to each maker, this page publishes ranges only; exact dimensions are confirmed on the drawing supplied with your quotation.
Frequently asked questions
No. Threaded inserts for plastics are manufacturer-specific: each catalog defines its own knurl geometry, lengths and recommended holes. The installed-hole series is broadly consistent across makes, but insert bodies are not interchangeable — the controlling document is the manufacturer drawing.
Only after qualification. Hole-size recommendations largely agree between catalogs, but knurl outside diameters and lengths differ (a 4-40 knurl OD runs 0.166 in. in one verified series and 0.172 in. in another), which changes retention. Send the drawing or part number you are replacing and test before production.
Verified catalog series run approximately 0.156 to 0.159 in. starting hole for 4-40, with the exact figure set by the insert style (straight press-in versus tapered heat-set), hole form and boss design — confirm against the drawing supplied with your quotation.
Heat-set (or ultrasonic) inserts are tapered and installed with heat or ultrasonic energy that re-melts the plastic into the knurls; press-in inserts have straight knurled bodies pressed cold into a plain hole. Both are machined here in brass; the right choice depends on the plastic and the pull-out and torque-out loads.
C36000 free-machining brass — the US twin of EN CW614N (CuZn39Pb3) — with tin or nickel plating on request. EN 10204 3.1 mill certificates accompany every shipment.