Inch (Unified) Thread Sizes & Tap Drills
| Size | UNC (coarse) TPI | UNC Tap Drill | UNF (fine) TPI |
|---|
| #4 | 40 | #43 | 48 |
| #6 | 32 | #36 | 40 |
| #8 | 32 | #29 | 36 |
| #10 | 24 | #25 | 32 |
| 1/4 | 20 | #7 | 28 |
| 5/16 | 18 | F | 24 |
| 3/8 | 16 | 5/16 | 24 |
| 7/16 | 14 | U | 20 |
| 1/2 | 13 | 27/64 | 20 |
| 9/16 | 12 | 31/64 | 18 |
| 5/8 | 11 | 17/32 | 18 |
| 3/4 | 10 | 21/32 | 16 |
| 7/8 | 9 | 49/64 | 14 |
| 1 | 8 | 7/8 | 12 |
Metric Coarse Threads & Tap Drills
| Size | Pitch (mm) | Tap Drill (mm) |
|---|
| M3 | 0.5 | 2.5 |
| M4 | 0.7 | 3.3 |
| M5 | 0.8 | 4.2 |
| M6 | 1.0 | 5.0 |
| M8 | 1.25 | 6.8 |
| M10 | 1.5 | 8.5 |
| M12 | 1.75 | 10.2 |
| M14 | 2.0 | 12.0 |
| M16 | 2.0 | 14.0 |
| M20 | 2.5 | 17.5 |
| M24 | 3.0 | 21.0 |
Bolt Grade & Property Class Markings
| Grade / Class | Head Marking | Min Tensile | Typical Use |
|---|
| SAE Grade 2 | No radial lines | 74 ksi (to 3/4") | General purpose, low stress |
| SAE Grade 5 | 3 radial lines | 120 ksi (to 1") | Automotive, machinery |
| SAE Grade 8 | 6 radial lines | 150 ksi | High-strength, drivetrain |
| Class 8.8 | "8.8" on head | 800 MPa | Metric standard structural |
| Class 10.9 | "10.9" on head | 1040 MPa | Metric high-strength |
| Class 12.9 | "12.9" on head | 1220 MPa | Socket cap screws, tooling |
Hex Bolt Head Size (Width Across Flats)
| Bolt Dia. | Wrench Size | Bolt Dia. | Wrench Size |
|---|
| 1/4 | 7/16 | 9/16 | 13/16 |
| 5/16 | 1/2 | 5/8 | 15/16 |
| 3/8 | 9/16 | 3/4 | 1-1/8 |
| 7/16 | 5/8 | 7/8 | 1-5/16 |
| 1/2 | 3/4 | 1 | 1-1/2 |
Approximate Tightening Torque (Dry, Plain Finish, ft-lb)
| Size (UNC) | Grade 5 | Grade 8 |
|---|
| 1/4-20 | 8 | 12 |
| 5/16-18 | 17 | 24 |
| 3/8-16 | 30 | 45 |
| 7/16-14 | 50 | 70 |
| 1/2-13 | 75 | 110 |
| 5/8-11 | 150 | 220 |
| 3/4-10 | 260 | 380 |
Torque values are approximate for dry, unlubricated, plain-finish fasteners and vary with plating, lubrication, and joint design. For critical joints, calculate from the actual application or test. Reference only — not engineering advice.
Metric Fine Threads & Tap Drills
| Size & Pitch | Tap Drill (mm) | Clearance (mm) |
|---|
| M6 × 0.75 | 5.25 | 6.6 |
| M8 × 1.0 | 7.00 | 9.0 |
| M8 × 1.25 (coarse) | 6.80 | 9.0 |
| M10 × 1.0 | 9.00 | 11.0 |
| M10 × 1.25 | 8.80 | 11.0 |
| M12 × 1.25 | 10.80 | 13.5 |
| M12 × 1.5 | 10.50 | 13.5 |
| M14 × 1.5 | 12.50 | 15.5 |
| M16 × 1.5 | 14.50 | 17.5 |
| M18 × 1.5 | 16.50 | 20.0 |
| M20 × 1.5 | 18.50 | 22.0 |
| M22 × 1.5 | 20.50 | 24.0 |
| M24 × 2.0 | 22.00 | 26.0 |
Tap drill for a metric thread is the major diameter minus the pitch. Clearance holes are ISO medium fit.
Drill Sizes — Decimal Equivalents
Number, letter and fractional drills in one place, smallest to largest.
Number Drills
| No. | Inch | No. | Inch | No. | Inch |
|---|
| 80 | 0.0135 | 76 | 0.02 | 72 | 0.025 |
| 70 | 0.028 | 68 | 0.031 | 65 | 0.035 |
| 60 | 0.04 | 56 | 0.0465 | 54 | 0.055 |
| 53 | 0.0595 | 52 | 0.0635 | 51 | 0.067 |
| 50 | 0.07 | 49 | 0.073 | 48 | 0.076 |
| 47 | 0.0785 | 46 | 0.081 | 45 | 0.082 |
| 44 | 0.086 | 43 | 0.089 | 42 | 0.0935 |
| 41 | 0.096 | 40 | 0.098 | 39 | 0.0995 |
| 38 | 0.1015 | 37 | 0.104 | 36 | 0.1065 |
| 35 | 0.11 | 34 | 0.111 | 33 | 0.113 |
| 32 | 0.116 | 31 | 0.12 | 30 | 0.1285 |
| 29 | 0.136 | 28 | 0.1405 | 27 | 0.144 |
| 26 | 0.147 | 25 | 0.1495 | 24 | 0.152 |
| 23 | 0.154 | 22 | 0.157 | 21 | 0.159 |
| 20 | 0.161 | 19 | 0.166 | 18 | 0.1695 |
| 17 | 0.173 | 16 | 0.177 | 15 | 0.18 |
| 14 | 0.182 | 13 | 0.185 | 12 | 0.189 |
| 11 | 0.191 | 10 | 0.1935 | 9 | 0.196 |
| 8 | 0.199 | 7 | 0.201 | 6 | 0.204 |
| 5 | 0.2055 | 4 | 0.209 | 3 | 0.213 |
| 2 | 0.221 | 1 | 0.228 | | |
Letter Drills
| Ltr | Inch | Ltr | Inch | Ltr | Inch |
|---|
| A | 0.234 | B | 0.238 | C | 0.242 |
| D | 0.246 | E | 0.25 | F | 0.257 |
| G | 0.261 | H | 0.266 | I | 0.272 |
| J | 0.277 | K | 0.281 | L | 0.29 |
| M | 0.295 | N | 0.302 | O | 0.316 |
| P | 0.323 | Q | 0.332 | R | 0.339 |
| S | 0.348 | T | 0.358 | U | 0.368 |
| V | 0.377 | W | 0.386 | X | 0.397 |
| Y | 0.404 | Z | 0.413 | | |
Fractional Drills
| Fraction | Inch | Fraction | Inch | Fraction | Inch |
|---|
| 1/64 | 0.0156 | 1/32 | 0.0313 | 3/64 | 0.0469 |
| 1/16 | 0.0625 | 5/64 | 0.0781 | 3/32 | 0.0938 |
| 7/64 | 0.1094 | 1/8 | 0.125 | 9/64 | 0.1406 |
| 5/32 | 0.1563 | 11/64 | 0.1719 | 3/16 | 0.1875 |
| 13/64 | 0.2031 | 7/32 | 0.2188 | 15/64 | 0.2344 |
| 1/4 | 0.25 | 17/64 | 0.2656 | 9/32 | 0.2813 |
| 19/64 | 0.2969 | 5/16 | 0.3125 | 21/64 | 0.3281 |
| 11/32 | 0.3438 | 23/64 | 0.3594 | 3/8 | 0.375 |
| 25/64 | 0.3906 | 13/32 | 0.4063 | 27/64 | 0.4219 |
| 7/16 | 0.4375 | 29/64 | 0.4531 | 15/32 | 0.4688 |
| 31/64 | 0.4844 | 1/2 | 0.5 | 17/32 | 0.5313 |
| 9/16 | 0.5625 | 19/32 | 0.5938 | 5/8 | 0.625 |
| 21/32 | 0.6563 | 11/16 | 0.6875 | 23/32 | 0.7188 |
| 3/4 | 0.75 | 25/32 | 0.7813 | 13/16 | 0.8125 |
| 27/32 | 0.8438 | 7/8 | 0.875 | 29/32 | 0.9063 |
| 15/16 | 0.9375 | 31/32 | 0.9688 | 1 | 1 |
Flat Washer Dimensions (Inch)
| Bolt Size | SAE ID | SAE OD | SAE Thk | USS ID | USS OD | USS Thk |
|---|
| 1/4 | 9/32 | 5/8 | .065 | 5/16 | 3/4 | .083 |
| 5/16 | 11/32 | 11/16 | .065 | 3/8 | 7/8 | .083 |
| 3/8 | 13/32 | 13/16 | .065 | 7/16 | 1 | .083 |
| 7/16 | 15/32 | 59/64 | .065 | 1/2 | 1-1/4 | .083 |
| 1/2 | 17/32 | 1-1/16 | .095 | 9/16 | 1-3/8 | .109 |
| 5/8 | 21/32 | 1-5/16 | .095 | 11/16 | 1-3/4 | .134 |
| 3/4 | 13/16 | 1-15/32 | .134 | 13/16 | 2 | .148 |
| 7/8 | 15/16 | 1-3/4 | .134 | 15/16 | 2-1/4 | .165 |
| 1 | 1-1/16 | 2 | .134 | 1-1/16 | 2-1/2 | .165 |
SAE washers are narrower with a smaller outside diameter; USS washers are wider and thicker for a larger bearing surface. Nominal dimensions per ASME B18.22.1.
Hex Nut Dimensions (Inch)
| Size | Across Flats | Finished Nut Thickness | Jam Nut Thickness |
|---|
| 1/4-20 | 7/16 | 7/32 | 5/32 |
| 5/16-18 | 1/2 | 17/64 | 3/16 |
| 3/8-16 | 9/16 | 21/64 | 7/32 |
| 7/16-14 | 11/16 | 3/8 | 1/4 |
| 1/2-13 | 3/4 | 7/16 | 5/16 |
| 9/16-12 | 7/8 | 31/64 | 5/16 |
| 5/8-11 | 15/16 | 35/64 | 3/8 |
| 3/4-10 | 1-1/8 | 41/64 | 27/64 |
| 7/8-9 | 1-5/16 | 3/4 | 31/64 |
| 1-8 | 1-1/2 | 55/64 | 35/64 |
Socket Head Cap Screw Dimensions (Inch)
| Size | Head Diameter | Head Height | Hex Key |
|---|
| #6-32 | .226 | .138 | 7/64 |
| #8-32 | .270 | .164 | 9/64 |
| #10-24 | .312 | .190 | 5/32 |
| 1/4-20 | .375 | .250 | 3/16 |
| 5/16-18 | .469 | .312 | 1/4 |
| 3/8-16 | .562 | .375 | 5/16 |
| 7/16-14 | .656 | .437 | 3/8 |
| 1/2-13 | .750 | .500 | 3/8 |
| 5/8-11 | .938 | .625 | 1/2 |
| 3/4-10 | 1.125 | .750 | 5/8 |
| 1-8 | 1.500 | 1.000 | 3/4 |
Per ASME B18.3. Hex key size is the nominal across-flats of the socket.
Clearance Hole Sizes (Inch)
| Bolt Size | Close Fit | Normal Fit | Loose Fit |
|---|
| #6 | .144 (#27) | .150 (#25) | .157 (#22) |
| #8 | .169 (#18) | .177 (#16) | .185 (#13) |
| #10 | .196 (#9) | .201 (#7) | .209 (#4) |
| 1/4 | .257 (F) | .266 (H) | .281 (9/32) |
| 5/16 | .323 (P) | .332 (Q) | .348 (S) |
| 3/8 | .386 (W) | .397 (X) | .413 (Z) |
| 7/16 | .4531 (29/64) | .4687 (15/32) | .4844 (31/64) |
| 1/2 | .5156 (33/64) | .5312 (17/32) | .5625 (9/16) |
| 5/8 | .6406 (41/64) | .6562 (21/32) | .6875 (11/16) |
| 3/4 | .7656 (49/64) | .7812 (25/32) | .8125 (13/16) |
Every figure on this page comes from published industry standards — SAE, ASTM, ANSI and ASME. Dimensions are nominal and exclude tolerances; consult the governing standard for tolerance limits. Reference only, not engineering advice.
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