UNCcoarse60° flankASME B1.1

5/16-18 UNC Thread Dimensions

5/16-18 UNC is a coarse Unified National Coarse thread. There are 18 threads per inch on a 0.3126 in major diameter, giving a metric-equivalent pitch of 1.411 mm. The recommended tap drill leaves roughly 75% thread engagement.

Major Ø0.3126 in
Threads per inch18
Pitch (metric)1.411 mm
Pitch Ø0.2764 in
Tap drill0.2571 in

Thread profile

millimetres unless stated
Thread profile — 5/16-18 UNCd 7.94d2 7.02d3 6.21mm60°P 1.411h3 0.866tap ⌀6.53
5/16-18 UNC — basic profile60° flank angle · Not to scale

Basic information

Designation
5/16-18 UNC
Thread system
Unified National Coarse
Series
coarse
Standard
ASME B1.1
Basic profile
Unified basic profile
Flank angle
60°

Dimensions

Major diameter
0.3126 in / 7.94 mm
Pitch (metric equivalent)
1.411 mm
Threads per inch
18
Pitch diameter
0.2764 in / 7.02 mm
Minor diameter (external)
0.2445 in / 6.21 mm
Minor diameter (internal)
0.2524 in / 6.41 mm
Thread depth
0.0341 in / 0.866 mm
Recommended tap drill
Ø 0.2571 in / 6.53 mm

How these values are derived

computed from the basic profile

These figures follow the Unified basic profile of ASME B1.1. A 60° basic profile uses a fundamental triangle height H = 0.866025 × P, with external minor diameter d₃ = d − 1.226869 × P and internal minor diameter D₁ = d − 1.082532 × P; the two differ because the external root is rounded while the internal crest is truncated. A 55° Whitworth profile uses H = 0.960491 × P and a thread height of 0.640327 × P. The recommended tap drill is given as nominal diameter minus pitch, which approximates 75% thread engagement — adjust it for tough materials or deep holes.

Compatible parts16 specification pages

All 5/16-18 fasteners

Every fastener below is threaded 5/16-18 UNC, so a nut, bolt or washer picked from this list will mate with it.

ASME B18.2.1ASME B18.3ASME B18.2.2
SpecificationLength
ASME B18.2.1 5/16-18 × 0.75 Hex Head Cap Screw — Inch Series0.0295 in
ASME B18.2.1 5/16-18 × 1 Hex Head Cap Screw — Inch Series0.0394 in
ASME B18.2.1 5/16-18 × 1.25 Hex Head Cap Screw — Inch Series0.0492 in
ASME B18.2.1 5/16-18 × 1.5 Hex Head Cap Screw — Inch Series0.0591 in
ASME B18.2.1 5/16-18 × 2 Hex Head Cap Screw — Inch Series0.0787 in
ASME B18.2.1 5/16-18 × 2.5 Hex Head Cap Screw — Inch Series0.0984 in
ASME B18.2.1 5/16-18 × 3 Hex Head Cap Screw — Inch Series0.1181 in
ASME B18.2.1 5/16-18 × 4 Hex Head Cap Screw — Inch Series0.1575 in
ASME B18.3 5/16-18 × 0.75 Socket Head Cap Screw — Inch Series0.0295 in
ASME B18.3 5/16-18 × 1 Socket Head Cap Screw — Inch Series0.0394 in
ASME B18.3 5/16-18 × 1.25 Socket Head Cap Screw — Inch Series0.0492 in
ASME B18.3 5/16-18 × 1.5 Socket Head Cap Screw — Inch Series0.0591 in
ASME B18.3 5/16-18 × 2 Socket Head Cap Screw — Inch Series0.0787 in
ASME B18.3 5/16-18 × 2.5 Socket Head Cap Screw — Inch Series0.0984 in
ASME B18.3 5/16-18 × 3 Socket Head Cap Screw — Inch Series0.1181 in
ASME B18.2.2 5/16-18 Hex Nut — Inch Series—

Related

Neighbouring sizes in Unified National Coarse.

#8-32 UNC#10-24 UNC#12-24 UNC1/4-20 UNC3/8-16 UNC7/16-14 UNC1/2-13 UNC9/16-12 UNC