Free Printable Bolt & Thread Gauge

Print at 100% and compare a mystery fastener with metric and SAE thread patterns, nominal diameter lines, and head-size outlines. This paper aid is approximate: verify the printed scale, then confirm close matches and safety-critical replacements with proper tools and the manufacturer's specification. Free, with no login.

Print it at 100% — or the measurements will be wrong

This only works if your printer does NOT scale the page. In the print dialog choose "Actual Size" or "100%", never "Fit to Page". Then check the printed 100 mm and 4-inch marks against a separate ruler. If either differs, reprint without scaling. Paper is an approximate comparison aid; confirm close matches, fine pitches and critical parts with calipers, a steel gauge and the manufacturer's specification.

How to use the gauge

1. Print page 1 at 100% and verify the rulers. 2. Thread pitch: visually align several crests with a printed pattern, then confirm close matches with a steel gauge. 3. Diameter: overlay the shank or thread crests on a nominal line pair, then confirm with calipers. 4. Wrench size: overlay the head on a hex outline, align opposite flats and test the socket on the actual head.

What's on the gauge

Thread-pitch patterns for metric (0.5, 0.7, 0.8, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5 mm) and selected SAE UNC/UNF pitches (10 to 24 threads per inch); nominal diameter line pairs from M3 to M16 and #8 to 1/2 inch; across-flats head outlines from 8 to 19 mm and 7/16 to 3/4 inch; and mm and inch rulers to check the printed scale against an external ruler. Page two adds size-to-pitch-to-socket reference tables for metric coarse and fine threads and SAE UNC and UNF.

Letter and A4 — same scale

Two versions are provided: US Letter (8.5 x 11 in) and A4 (210 x 297 mm). The gauges print at identical physical scale in both — only the surrounding paper differs — so use whichever your printer is loaded with. Both are free to download, print, and share.

Related lookups

Loading interactive lookup…