MAN4MACHINEDesignation calculator
1/4-20 UNC-2A in, every dimension out.
A callout is a nominal size (a gauge number or a fraction), a TPI -- required for constant-pitch UN/UNR/UNJ, assumed standard for UNC/UNF/UNEF otherwise -- a series, and an optional tolerance class: a grade digit for how tight the fit is, and A or B for external or internal. Type any of it below.
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
- Major diameter
- 0.2500"
- Pitch diameter
- 0.2175"
- Minor diameter
- 0.1959"
Clearance (normal)
- Clearance drill
- 9/32" (0.2813")