Home › References › Measurement › Thread Sizes 🔧 Thread Sizes Reference Bolt and screw thread specifications for Unified National Coarse (UNC) and Metric (ISO) thread standards. Each entry includes major diameter, thread pitch, and recommended tap drill size.
Unified National Coarse (UNC) Threads Size Major Diam. (in) TPI Tap Drill #0-80 0.0600 80 #56 (0.0465") #1-64 0.0730 64 #53 (0.0595") #2-56 0.0860 56 #50 (0.0700") #3-48 0.0990 48 #47 (0.0785") #4-40 0.1120 40 #43 (0.0890") #6-32 0.1380 32 #36 (0.1065") #8-32 0.1640 32 #29 (0.1360") #10-24 0.1900 24 #25 (0.1495") #12-24 0.2160 24 #16 (0.1770") 1/4-20 0.2500 20 #7 (0.2010") 5/16-18 0.3125 18 F (0.2570") 3/8-16 0.3750 16 5/16" (0.3125") 7/16-14 0.4375 14 U (0.3680") 1/2-13 0.5000 13 27/64" (0.4219") 9/16-12 0.5625 12 31/64" (0.4844") 5/8-11 0.6250 11 17/32" (0.5313") 3/4-10 0.7500 10 21/32" (0.6563") 7/8-9 0.8750 9 49/64" (0.7656") 1-8 1.0000 8 7/8" (0.8750")
Metric (ISO) Threads — Coarse Pitch Size Pitch (mm) Major Diam. (mm) Tap Drill M1 0.25 1.0 0.75 mm M1.2 0.25 1.2 0.95 mm M1.6 0.35 1.6 1.25 mm M2 0.40 2.0 1.60 mm M2.5 0.45 2.5 2.05 mm M3 0.50 3.0 2.50 mm M4 0.70 4.0 3.30 mm M5 0.80 5.0 4.20 mm M6 1.00 6.0 5.00 mm M8 1.25 8.0 6.75 mm M10 1.50 10.0 8.50 mm M12 1.75 12.0 10.25 mm M14 2.00 14.0 12.00 mm M16 2.00 16.0 14.00 mm M18 2.50 18.0 15.50 mm M20 2.50 20.0 17.50 mm M24 3.00 24.0 21.00 mm M30 3.50 30.0 26.50 mm