MAN4MACHINEANSI / ASME B1.1 thread database
UNC, UNF, UNEF, UN, UNR, and UNJ -- the Unified Thread Standard counts threads per inch (TPI) rather than pitch in millimeters. Type a callout exactly as it appears on the print, tolerance class and all, and every basic dimension and tap drill recomputes instantly.
Class 2 (Standard), external thread. This class carries a systematic allowance -- a deliberate minimum clearance below basic size.
Try “1/4-20 UNC-2A”, “#10-32 UNF”, or “1-8 UN-3A”. Add “LH” for a left-hand thread.
Basic (theoretical) dimensions and a shop tap drill only -- ASME B1.1's exact Class 1A/2A/3A pitch diameter limits depend on length of thread engagement as well as grade. Consult the standard or a calibrated thread gauge for gauge-critical work.
Calculated live
Basic dimensions
Clearance (normal)
Did you know
The largest screw ever made
As the story is told in engineering circles, the largest screw thread ever cut was made in 1967 at the Penrith Engineering Works in Scotland: roughly 27.4 feet long, 4.2 feet in diameter, and weighing about 12.6 metric tons. Take it as shop-floor legend rather than a standards citation -- but it's a fun one to picture next to a #0-80 screw on the size chart below.
Penrith Engineering Works, Scotland, 1967 (as reported)Graduated pitch
One TPI per diameter, getting finer from UNC through UNF to UNEF -- pick the series the application calls for, not just the default.
Constant pitch
One TPI held across a range of diameters, with UNR and UNJ adding a controlled root radius for fatigue life over plain UN.
UNC· Coarse
UNF· Fine
UN· Constant Pitch
UNR· Controlled Root
In 1841, engineer Joseph Whitworth proposed a single national thread standard for Britain: a 55 degree included angle with a rounded crest and root. Adopted as the British Standard Whitworth (BSW), it was the first national screw thread standard anywhere in the world.
Joseph Whitworth, 1841Want to start from a blank designation instead of browsing? Open the full calculator → · Read the full history & trivia page →