Specification summary of ASME B18.6.3 as applied to slotted pan head machine screws, unc: the dimensions the standard controls, the full specified size range, and the equivalent DIN/ISO/ASME designations.
ASME B18.6.3 — Scope
ASME B18.6.3 is "Machine screws and machine screw nuts (inch series)". An inch-series document; sizes are numbered gauges and fractional inches, not metric.
Material, property class, surface finish and packaging are governed by separate documents — ISO 898-1 and ISO 898-2 for mechanical property classes, ISO 4042 for electroplated finishes.
Tolerance & Product Grades
ASME B18.6.3 does not divide slotted pan head machine screws, unc into product grades. Tolerances are given as limits on the individual dimensions in the table.
Where a general-tolerance class is cited on the drawing instead, it applies to the dimensions not otherwise toleranced.
Dimensions Specified by ASME B18.6.3
| Size | Pitch P (in) | Head diameter dk (in) | Head height k (in) | R (in) | J (in) | T (in) | Length range l (in) | Reference standard |
|---|---|---|---|---|---|---|---|---|
| #0 | 0.013 | 0.116 | 0.039 | 0.02 | 0.023 | 0.022 | 1/16"~1 1/2" | ASME B18.6.3 |
| #1 | 0.016 | 0.142 | 0.046 | 0.025 | 0.026 | 0.027 | 1/16"~1 1/2" | ASME B18.6.3 |
| #2 | 0.018 | 0.167 | 0.053 | 0.035 | 0.031 | 0.031 | 1/16"~2 1/2" | ASME B18.6.3 |
| #3 | 0.021 | 0.193 | 0.06 | 0.037 | 0.035 | 0.036 | 1/8"~2 1/2" | ASME B18.6.3 |
| #4 | 0.025 | 0.219 | 0.068 | 0.042 | 0.039 | 0.04 | 1/8"~4" | ASME B18.6.3 |
| #5 | 0.025 | 0.245 | 0.075 | 0.044 | 0.043 | 0.045 | 3/16"~4" | ASME B18.6.3 |
| #6 | 0.031 | 0.27 | 0.082 | 0.046 | 0.048 | 0.05 | 1/8"~4" | ASME B18.6.3 |
| #8 | 0.031 | 0.322 | 0.096 | 0.052 | 0.054 | 0.058 | 1/8"~5" | ASME B18.6.3 |
| #10 | 0.042 | 0.373 | 0.11 | 0.061 | 0.06 | 0.068 | 3/16"~8" | ASME B18.6.3 |
| #12 | 0.042 | 0.425 | 0.125 | 0.078 | 0.067 | 0.077 | 1/4"~8" | ASME B18.6.3 |
| 1/4" | 0.05 | 0.492 | 0.144 | 0.087 | 0.075 | 0.087 | 3/8"~10" | ASME B18.6.3 |
| 5/16" | 0.056 | 0.615 | 0.178 | 0.099 | 0.084 | 0.106 | 1/2"~10" | ASME B18.6.3 |
| 3/8" | 0.062 | 0.74 | 0.212 | 0.143 | 0.094 | 0.124 | 1/2"~12" | ASME B18.6.3 |
| 7/16" | 0.071 | 0.863 | 0.247 | 0.153 | 0.094 | 0.142 | 3/4"~12" | ASME B18.6.3 |
| 1/2" | 0.077 | 0.987 | 0.281 | 0.175 | 0.106 | 0.161 | 3/4"~12" | ASME B18.6.3 |
| 9/16" | 0.083 | 1.041 | 0.315 | 0.197 | 0.118 | 0.179 | 3/4"~12" | ASME B18.6.3 |
| 5/8" | 0.091 | 1.172 | 0.35 | 0.219 | 0.133 | 0.197 | 3/4"~14" | ASME B18.6.3 |
| 3/4" | 0.1 | 1.435 | 0.419 | 0.263 | 0.149 | 0.234 | 1"~14" | ASME B18.6.3 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Slotted Pan Head Machine Screws, UNC page.
Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ASME B18.6.3
ASME B18.6.3 is the inch-based reference; for metric programs choose the ISO equivalent instead.
Custom manufacturing · Made to drawing
Need a screw to this standard in a non-standard size?
Parts built to ASME B18 6 3 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
