ASME B18.3 Socket Set Screw Dimensions Chart — Inch

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ASME B18.3 socket set screw dimensions — Table 14

ASME B18.3 specifies hexagon socket set screw dimensions in the inch series: one hex socket size J per screw diameter, minimum key engagement T, a single point-diameter column C shared by cup and flat points, half-dog point diameter P and length Q, and the length threshold at which the cone point switches from 118° to 90°.

ASME B18.3 hex socket set screw dimensions — socket J, key engagement T, point diameter C, half-dog P and Q, cone point angles

Socket J, engagement T, point diameter C, half-dog P/Q and cone-point insets as charted below.

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). Threads UNC/UNF, class 3A per ASME B1.1.

Oval point radius R

#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, per B18.3.

Governing document: ASME B18.3 (Tables 14–16), corroborated line-by-line against the MSC Direct B18.3 socket set screw reference tables (verified July 2026).

Catalog caution — optional cup points (Table 16)

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 chart above publishes the standard Table 14 values; knurled or locking cup points are machined to drawing.

Need these set screws in brass?

Product

UNC Brass Socket Set Screws

Cup, flat, cone and half-dog points, #4–1/2 in., machined to ASME B18.3 in C36000.

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Imperial & ANSI Brass Parts

The full UNC/UNF/NPT range — nuts, set screws, standoffs, inserts and flare nuts.

View → Metric equivalent

DIN 913–916 Brass Set Screws

The metric grub screw range — ISO 4026–4029.

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More reference charts & tools

Chart

ASME B18.2.2 Hex Nut Dimensions

Inch hex and jam nut chart, 1/4–3/4 in.

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Thread Size Chart

UNC/UNF, metric, BSP and NPT thread dimensions side by side.

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Tap Drill Chart

Tap-drill sizes for metric, UNC, BSP (G) and NPT threads.

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Frequently asked questions

What does ASME B18.3 specify for set screws?

ASME B18.3 specifies the dimensions of inch-series hexagon socket set screws: one hex socket size J per screw diameter, minimum key engagement T, a shared diameter column C for cup and flat points, half-dog point diameter P and length Q, oval-point radius R (0.75 × basic diameter), and the length threshold at which the cone point changes from 118° to 90°.

What hex key fits a 1/4 in. socket set screw?

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.

Do cup point and flat point set screws share the same point diameter?

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.

When is a cone point 90 degrees versus 118 degrees?

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.

Does ASTM F912 apply to brass set screws?

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; the standard governs geometry, not the alloy.

Last reviewed: July 2026. This chart is a reference summary — verify against the governing standard and your drawing for procurement-critical work.

ASME B18.3 Socket Set Screw Dimensions