Data Sources & Provenance
BenchReference publishes only values that trace to a recognized standard or an established engineering reference. The canonical data lives as version-controlled structured files; every change is reviewable, and automated validation runs before every deployment (uniqueness, ordering, unit-derivation, and engagement-range checks across 309 drills and 65 threads).
Standards
| Standard | Organization | Used for |
|---|---|---|
| ASME B94.11M — Twist Drills | ASME | Standard twist drill diameters: fractional-inch, number (wire gauge), letter, and metric series. |
| ASME B1.1 — Unified Inch Screw Threads (UN and UNR Thread Form) | ASME | Basic dimensions of Unified National Coarse (UNC) and Fine (UNF) threads. |
| ISO 261 / ISO 724 — ISO general purpose metric screw threads | ISO | Basic dimensions (nominal diameter, pitch) of ISO metric coarse and fine threads. |
| ISO 273 — Fasteners: clearance holes for bolts and screws | ISO | Clearance hole diameters (close, medium, free series) for metric fasteners. |
| ISO 2306 — Drills for use prior to tapping screw threads | ISO | Recommended tap drill sizes for ISO metric threads. |
| ASME B18.2.8 — Clearance Holes for Bolts, Screws, and Studs | ASME | Recommended clearance-hole drills (close, normal, loose fits) for inch fasteners. |
| ASME B18.2.1 — Square, Hex, Heavy Hex, and Askew Head Bolts and Hex Cap Screws | ASME | Hex cap screw head dimensions: width across flats (wrench size) and head height. |
| ASME B18.2.2 — Nuts for General Applications | ASME | Finished hex nut dimensions: width across flats and thickness. |
| ISO 4014 / ISO 4017 — Hexagon head bolts and screws | ISO | Metric hex bolt dimensions: width across flats (s) and head height (k). |
| ISO 4032 — Hexagon regular nuts (style 1) | ISO | Metric hex nut dimensions: width across flats and height (m). |
References
- Machinery’s Handbook — tap drill charts (Industrial Press) — The conventional ~75% thread-engagement tap drill chart used across the industry.
Accuracy rules
- Each dimension is stored once, in its canonical unit; the other unit is derived with the exact definition 1 in = 25.4 mm.
- Nearest-size comparisons run at full precision — values are never rounded before comparison, only for display.
- Values that cannot be reliably sourced are omitted and marked “—”, never estimated.
- Tap drill recommendations are the conventional ≈75%-engagement chart values, labeled as guidance rather than the only correct choice.
- Permanent dimensional data (drill diameters, thread geometry) is kept separate from anything that could change (codes, ratings, compatibility claims) — V1 contains only the former.
Corrections
Found a value that disagrees with the governing standard? Corrections are versioned and logged in the public revision history. Contact: hello@benchreference.com.