Identify an Allen / Hex Key Size
A free tool for identifying an Allen wrench whose size you do not know. Lay the hex key on a calibrated on-screen ruler, or print a 1:1 paper gauge, and read its across-flats size as a metric or SAE inch size — no caliper or wrench set needed.
How to identify a hex key
1
Pick a mode
Choose "Measure on screen" for a calibrated ruler, or "Print a gauge" to download a paper sheet.
2
Calibrate or print at 100%
On screen, match the blue rectangle to a bank card. On paper, print at Actual size and check the 50 mm bar.
3
Measure and read
Lay the hex key flat across the scale — flat side down — and read the across-flats size; the tool shows metric and SAE.
Read an Allen key's across-flats size in metric and inch
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