Choose a reference: convert units or look up socket screw dimensions to prepare your parts and assemblies.
Use length conversion to interpret drawings and prepare dimensions for machining or dimensional inspection.
Related: CNC Machining · Dimensional Inspection
Convert the area of sheet or plate when preparing the material required for a part. This does not calculate cutting waste.
Related: Manufacturing
Convert a part volume obtained from CAD. Volume alone does not determine print time, infill, mould capacity or a quotation.
Related: 3D Printing · Plastic Injection
Convert a known part or material mass. No density is assumed; kg and lb here are mass units, not force units.
Related: Manufacturing
Compare sheet or plate mass per area from a material specification. This is not pressure and does not convert sheet gauges to thickness.
Related: Manufacturing
| Fraction (in) | Decimal (in) | mm |
|---|---|---|
| 1/16 | 0.0625 | 1.5875 |
| 1/8 | 0.125 | 3.175 |
| 1/4 | 0.25 | 6.35 |
| 3/8 | 0.375 | 9.525 |
| 1/2 | 0.5 | 12.7 |
| 3/4 | 0.75 | 19.05 |
| 1 | 1 | 25.4 |
Include the drawing or CAD, units, material, quantity and critical dimensions. If you only have the physical part, identify worn areas and explain its function.
A scanned mesh records the existing surface. Reconstructing a reusable CAD model requires interpreting geometry and wear.
Related: Reverse Engineering · 3D Scanning
1 inch is exactly 25.4 mm. Area and volume factors are squared and cubed respectively. For example, 1 in² = 645.16 mm².
A fraction rounded to 1/16 inch does not replace a nominal dimension or its tolerance. Retain the original specification when preparing or inspecting the part.
Related: Dimensional Inspection
Conversion references: NIST — SI Units: Length · NIST SP 811, Appendix B. The tool uses 1 lb = 0.45359237 kg and 1 ft = 0.3048 m.
Select a series and size. These are screw dimensions, not clearance-hole or counterbore dimensions.
Head angle: cylindrical head, flat bearing surface.
| Size | d nominalmm | PPitch · mm | Head ØMax. · mm | Head heightMax. · mm | Hex keyNominal · mm |
|---|---|---|---|---|---|
| M3 | 3 | 0.5 | 5.68 | 3 | 2.5 |
| M4 | 4 | 0.7 | 7.22 | 4 | 3 |
| M5 | 5 | 0.8 | 8.72 | 5 | 4 |
| M6 | 6 | 1 | 10.22 | 6 | 5 |
| M8 | 8 | 1.25 | 13.27 | 8 | 6 |
| M10 | 10 | 1.5 | 16.27 | 10 | 8 |
| M12 | 12 | 1.75 | 18.27 | 12 | 10 |
| M14 | 14 | 2 | 21.33 | 14 | 12 |
| M16 | 16 | 2 | 24.33 | 16 | 14 |
| M20 | 20 | 2.5 | 30.33 | 20 | 17 |
| M24 | 24 | 3 | 36.39 | 24 | 19 |
Source: Fastenal · REV-03 · 2023 · Additional dimensional reference.
Head angle: cylindrical head, flat bearing surface.
| Size | d nominalin | Head ØMax. · in | Head heightMax. · in | Hex keyNominal · in |
|---|---|---|---|---|
| #4 | 0.112 | 0.183 | 0.112 | 3/32 |
| #5 | 0.125 | 0.205 | 0.125 | 3/32 |
| #6 | 0.138 | 0.226 | 0.138 | 7/64 |
| #8 | 0.164 | 0.27 | 0.164 | 9/64 |
| #10 | 0.19 | 0.312 | 0.19 | 5/32 |
| 1/4 | 0.25 | 0.375 | 0.25 | 3/16 |
| 5/16 | 0.3125 | 0.469 | 0.312 | 1/4 |
| 3/8 | 0.375 | 0.562 | 0.375 | 5/16 |
| 7/16 | 0.4375 | 0.656 | 0.438 | 3/8 |
| 1/2 | 0.5 | 0.75 | 0.5 | 3/8 |
| 5/8 | 0.625 | 0.938 | 0.625 | 1/2 |
| 3/4 | 0.75 | 1.125 | 0.75 | 5/8 |
Source: Nickel Systems.
Length L runs from the underside of the head to the end of the screw. Head height is additional.
Confirm thread pitch or TPI, length, tolerances and supplier specification. An inch screw converted to mm is still an inch-series screw. Head size alone does not identify its thread.
Related: Engineering · CNC Machining. Reference for preparing parts and fixtures; this is not a screw sales catalogue.
Open unit converterSelect a series and size. These are screw dimensions, not clearance-hole or counterbore dimensions.
DIN 7991 is a withdrawn standard still used in commercial specifications. This table is specifically DIN 7991; do not substitute it for ISO 10642. The current ISO edition is ISO 10642:2026.
Head angle: 90° (+2°/−0°).
| Size | d nominalmm | PPitch · mm | Head ØMax. · mm | Head heightMax. · mm | Hex keyNominal · mm |
|---|---|---|---|---|---|
| M3 | 3 | 0.5 | 6 | 1.7 | 2 |
| M4 | 4 | 0.7 | 8 | 2.3 | 2.5 |
| M5 | 5 | 0.8 | 10 | 2.8 | 3 |
| M6 | 6 | 1 | 12 | 3.3 | 4 |
| M8 | 8 | 1.25 | 16 | 4.4 | 5 |
| M10 | 10 | 1.5 | 20 | 5.5 | 6 |
| M12 | 12 | 1.75 | 24 | 6.5 | 8 |
| M14 | 14 | 2 | 27 | 7 | 10 |
| M16 | 16 | 2 | 30 | 7.5 | 10 |
| M18 | 18 | 2.5 | 33 | 8 | 12 |
| M20 | 20 | 2.5 | 36 | 8.5 | 12 |
Source: Fullerkreg · Additional dimensional reference.
Head angle: 82° nominal.
| Size | d nominalin | Head ØTheoretical max. · in | Head heightRef. · in | Hex keyNominal · in |
|---|---|---|---|---|
| #4 | 0.112 | 0.255 | 0.083 | 1/16 |
| #5 | 0.125 | 0.281 | 0.09 | 5/64 |
| #6 | 0.138 | 0.307 | 0.097 | 5/64 |
| #8 | 0.164 | 0.359 | 0.112 | 3/32 |
| #10 | 0.19 | 0.411 | 0.127 | 1/8 |
| 1/4 | 0.25 | 0.531 | 0.161 | 5/32 |
| 5/16 | 0.3125 | 0.656 | 0.198 | 3/16 |
| 3/8 | 0.375 | 0.781 | 0.234 | 7/32 |
| 7/16 | 0.4375 | 0.844 | 0.234 | 1/4 |
| 1/2 | 0.5 | 0.938 | 0.251 | 5/16 |
| 5/8 | 0.625 | 1.188 | 0.324 | 3/8 |
| 3/4 | 0.75 | 1.438 | 0.396 | 1/2 |
Source: Nickel Systems.
Length L includes the countersunk head, from the top face to the end of the screw.
Confirm thread pitch or TPI, length, tolerances and supplier specification. An inch screw converted to mm is still an inch-series screw. Head size alone does not identify its thread.
Related: Engineering · CNC Machining. Reference for preparing parts and fixtures; this is not a screw sales catalogue.
Open unit converterReference drill sizes before cutting internal threads with a cutting tap. Select the thread series; the drill column shows the recommended starting diameter.
| Thread | Nominal | Pitch / TPI | Tap drillmm |
|---|---|---|---|
| M3 × 0.5 | 3 | 0.5 | 2.5 |
| M4 × 0.7 | 4 | 0.7 | 3.3 |
| M5 × 0.8 | 5 | 0.8 | 4.2 |
| M6 × 1.0 | 6 | 1 | 5 |
| M8 × 1.25 | 8 | 1.25 | 6.8 |
| M10 × 1.5 | 10 | 1.5 | 8.5 |
| M12 × 1.75 | 12 | 1.75 | 10.2 |
Source: Gühring · Tap Drill Sizes Metric.
| Thread | Nominal | Pitch / TPI | Tap drillin |
|---|---|---|---|
| #4-40 UNC | #4 | 40 TPI | #43 · 0.0890 |
| #6-32 UNC | #6 | 32 TPI | #36 · 0.1065 |
| #8-32 UNC | #8 | 32 TPI | #29 · 0.1360 |
| #10-24 UNC | #10 | 24 TPI | #25 · 0.1495 |
| 1/4-20 UNC | 1/4 | 20 TPI | #7 · 0.2010 |
| 5/16-18 UNC | 5/16 | 18 TPI | F · 0.2570 |
| 3/8-16 UNC | 3/8 | 16 TPI | 5/16 · 0.3125 |
| 1/2-13 UNC | 1/2 | 13 TPI | 27/64 · 0.4219 |
Source: Gühring · Tap Drill Sizes UNC/UNF.
| Thread | Nominal | Pitch / TPI | Tap drillin |
|---|---|---|---|
| #4-48 UNF | #4 | 48 TPI | #42 · 0.0935 |
| #6-40 UNF | #6 | 40 TPI | #33 · 0.1130 |
| #8-36 UNF | #8 | 36 TPI | #29 · 0.1360 |
| #10-32 UNF | #10 | 32 TPI | #21 · 0.1590 |
| 1/4-28 UNF | 1/4 | 28 TPI | #3 · 0.2130 |
| 5/16-24 UNF | 5/16 | 24 TPI | I · 0.2720 |
| 3/8-24 UNF | 3/8 | 24 TPI | Q · 0.3320 |
| 1/2-20 UNF | 1/2 | 20 TPI | 29/64 · 0.4531 |
Source: Gühring · Tap Drill Sizes UNC/UNF.
These values are starting references for cutting taps. Material, tap geometry, tolerance class and thread engagement can change the final choice.
Verify the tap manufacturer recommendation and measure the actual drill. A tap drill is not a clearance hole for a bolt.
Related: CNC Machining · Engineering.