About BenchReference

BenchReference is an interactive handbook for the physical world. It answers the reference questions that come up at the bench, in the shop, and at the CAD screen:

• What exactly is a #7 drill, and what's the nearest metric equivalent?
• What tap drill does 1/4-20 need — and what are my options at other engagement levels?
• I measured 6.7 mm. Which standard drills are closest, and by how much?
• What clearance hole does an M8 bolt need?

The answers come from structured, validated data tied to recognized standards — not articles. Because a drill diameter or thread pitch doesn't change, these pages are built to remain correct and useful for decades. The defining test: could someone use this same page in 2076 and still find it useful?

Principles

• Data first, prose second. Tables, dimensions, and tools — explanation only where it helps.
• The answer comes first. No introductions above the numbers.
• Provenance is visible. Every important value cites its standard; see data sources.
• Deterministic math. All conversions and nearest-size calculations are exact code, covered by automated tests.
• No accounts, no popups. Reference tools work immediately, on any device, and print cleanly.

Current coverage and roadmap

Today: drill sizes (fractional, number, letter, metric), unified inch threads (UNC/UNF), ISO metric threads, tap drills, and clearance holes. Planned expansions, in order: fastener dimensions (head, wrench, and socket sizes), pipe/NPS dimensions, O-rings (AS568), bearings, and wire/sheet gauges.