UNC brass hex socket set screw (ASME B18.3) — engineering drawing (Brassland).
Specification
| Standard | ASME B18.3 (hexagon socket set screws, inch series) — dimensions |
| Points | Cup, flat, cone and half-dog on this page; oval point on request |
| Sizes | #4 to 1/2 in.; other sizes to your drawing |
| Thread | UNC / UNF, class 3A per ASME B1.1 |
| Material | C36000 free-machining brass (UNS) — EN twin CW614N (CuZn39Pb3); lead-free C69300 / CW724R on request — note: ASTM F912 is the alloy-steel material spec and does not apply to brass; brass screws are machined to B18.3 dimensions |
| Certificate | EN 10204 3.1 per shipment; 3.2 on request |
Datasheet — hex socket set screws to ASME B18.3 (Table 14)
| Size (basic dia) | Hex socket J | Min key engagement T | Cup & flat point dia C max / min | Half-dog dia P max / min | Half-dog length Q max / min | Cone point angle |
|---|---|---|---|---|---|---|
| #4 (0.1120) | 0.050 | 0.070 | 0.061 / 0.051 | 0.075 / 0.070 | 0.030 / 0.026 | 90° for L ≥ 0.19 |
| #6 (0.1380) | 1/16 (0.062) | 0.080 | 0.074 / 0.064 | 0.092 / 0.087 | 0.038 / 0.032 | 90° for L ≥ 0.19 |
| #8 (0.1640) | 5/64 (0.078) | 0.090 | 0.087 / 0.076 | 0.109 / 0.103 | 0.043 / 0.037 | 90° for L ≥ 0.25 |
| #10 (0.1900) | 3/32 (0.094) | 0.100 | 0.102 / 0.088 | 0.127 / 0.120 | 0.049 / 0.041 | 90° for L ≥ 0.25 |
| 1/4 (0.2500) | 1/8 (0.125) | 0.125 | 0.132 / 0.118 | 0.156 / 0.149 | 0.067 / 0.059 | 90° for L ≥ 0.31 |
| 5/16 (0.3125) | 5/32 (0.156) | 0.156 | 0.172 / 0.156 | 0.203 / 0.195 | 0.082 / 0.074 | 90° for L ≥ 0.38 |
| 3/8 (0.3750) | 3/16 (0.188) | 0.188 | 0.212 / 0.194 | 0.250 / 0.241 | 0.099 / 0.089 | 90° for L ≥ 0.44 |
| 1/2 (0.5000) | 1/4 (0.250) | 0.250 | 0.291 / 0.270 | 0.344 / 0.334 | 0.130 / 0.120 | 90° for L ≥ 0.57 |
Dimensions in inches per ASME B18.3, Table 14. Cone point: 118° on screws shorter than the listed length threshold. Key engagement T applies to screws at or above the shortest optimum length of Table 14; shorter (stub) screws have reduced engagement per Table 15. Cup and flat points share the single diameter column C; the cone point has no diameter spec (apex nominally sharp, slight flat or rounding permissible). Full dimension chart: ASME B18.3 socket set screw dimension chart →
Oval point radius R (per B18.3)
| #4 | #6 | #8 | #10 | 1/4 | 5/16 | 3/8 | 1/2 |
|---|---|---|---|---|---|---|---|
| 0.084 | 0.104 | 0.123 | 0.142 | 0.188 | 0.234 | 0.281 | 0.375 |
R in inches = 0.75 × basic screw diameter. Oval-point screws machined on request.
Catalog caution — optional cup points
B18.3 Table 16 also lists optional cup points (types B–G: knurled and self-locking forms) with smaller diameters than the standard Table 14 cup point — at 1/4 in., 0.125/0.114 versus 0.132/0.118. Some distributor charts print the Table 16 values in their “cup point” column, so two catalogs can disagree while both being right. The tables above publish the standard Table 14 values; if your drawing calls for a knurled or locking cup point, we machine to the drawing.
Applications
Brass socket set screws are chosen where corrosion resistance, electrical conductivity, a non-magnetic fastener or a softer, less-marring point matters — securing knobs, collars, pulleys and gears on shafts in instruments, valves and trim hardware, electrical and RF assemblies, and food or marine environments. The metric equivalents are on our brass set screws pages (DIN 913/914/915/916, ISO 4026–4029).
Imperial & UNC range
Related pages
DIN 913–916 / ISO 4026–4029 metric range.
View →MetricThe metric cup-point twin.
View →MaterialUS free-machining brass datasheet.
View →IndustryCollars, knobs and fittings.
View →ToolUNC tap drills at a glance.
View →GuideUNC / UNF, metric and BSP reference.
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
Socket, key-engagement and point dimensions extracted from ASME B18.3-2012, Tables 14–16, and corroborated line-by-line against the MSC Direct B18.3 socket set screw reference tables (verified July 2026). Governing document: ASME B18.3.
Frequently asked questions
1/8 in. — ASME B18.3 assigns socket size J per screw diameter: 0.050 in. at #4, 1/16 at #6, 5/64 at #8, 3/32 at #10, 1/8 at 1/4 in., 5/32 at 5/16, 3/16 at 3/8 and 1/4 at 1/2 in.
Yes — B18.3 Table 14 gives one diameter column C for both cup and flat points (0.132/0.118 at 1/4 in.). Note that the optional cup points of Table 16 (knurled, self-locking types) run smaller, which is why two catalogs can print different cup-point diameters.
The cone angle is 90 degrees on screws at or above a length threshold that scales with diameter (0.19 in. for #4 and #6, up to 0.57 in. at 1/2 in.) and 118 degrees on shorter screws, per ASME B18.3.
Brass is corrosion resistant, non-magnetic and electrically conductive, and its softer point is less likely to mar a shaft — useful on instrument spindles, trim hardware and plated or stainless shafts. For high preload torque, alloy steel per ASTM F912 remains the standard choice; we machine the brass version.
No — ASTM F912 is the material specification for alloy-steel socket set screws. Brass set screws are machined to the dimensions of ASME B18.3 from C36000 free-machining brass, with material certified to EN 10204 3.1 per shipment.