BenchReference

Thread, Tap Drill & Clearance Chart

Every thread links to a full reference page with dimensions, engagement options, and equivalents. Tap drills are the conventional chart recommendation (≈75% thread engagement); clearance holes are the close/normal/loose fits per ASME B18.2.8 (inch) and ISO 273 (metric). Have a callout to decode instead? Use the Thread Decoder. A printable PDF of this chart: tap-drill-chart.pdf.

Major Ø — the thread size Tap drill — to cut threads Clearance — to pass through 0.2500″ 1/4″-20 UNC bolt #7 drill (0.2010″), then tap bolt major Ø close 17/64″ normal 9/32″ loose 19/64″ widths at true relative scale — clearance is only slightly larger Drill the tap-drill size to make threads; drill the clearance size to let the bolt pass. Example row: 1/4″-20 UNC.

Unified inch threads (UNC / UNF)

Thread Major Ø TPI Tap drill Tap drill Ø Clearance close normal loose
#0-80 UNF 0.0600″ 80 3/64″ 0.0469″ #51 #48 3/32″
#1-64 UNC 0.0730″ 64 #53 0.0595″ #46 #43 #37
#1-72 UNF 0.0730″ 72 #53 0.0595″ #46 #43 #37
#2-56 UNC 0.0860″ 56 #50 0.0700″ 3/32″ #38 #32
#2-64 UNF 0.0860″ 64 #50 0.0700″ 3/32″ #38 #32
#3-48 UNC 0.0990″ 48 #47 0.0785″ #36 #32 #30
#3-56 UNF 0.0990″ 56 #45 0.0820″ #36 #32 #30
#4-40 UNC 0.1120″ 40 #43 0.0890″ #31 #30 #27
#4-48 UNF 0.1120″ 48 #42 0.0935″ #31 #30 #27
#5-40 UNC 0.1250″ 40 #38 0.1015″ 9/64″ 5/32″ 11/64″
#5-44 UNF 0.1250″ 44 #37 0.1040″ 9/64″ 5/32″ 11/64″
#6-32 UNC 0.1380″ 32 #36 0.1065″ #23 #18 #13
#6-40 UNF 0.1380″ 40 #33 0.1130″ #23 #18 #13
#8-32 UNC 0.1640″ 32 #29 0.1360″ #15 #9 #3
#8-36 UNF 0.1640″ 36 #29 0.1360″ #15 #9 #3
#10-24 UNC 0.1900″ 24 #25 0.1495″ #5 #2 B
#10-32 UNF 0.1900″ 32 #21 0.1590″ #5 #2 B
#12-24 UNC 0.2160″ 24 #16 0.1770″ — — —
#12-28 UNF 0.2160″ 28 #14 0.1820″ — — —
1/4″-20 UNC 0.2500″ 20 #7 0.2010″ 17/64″ 9/32″ 19/64″
1/4″-28 UNF 0.2500″ 28 #3 0.2130″ 17/64″ 9/32″ 19/64″
5/16″-18 UNC 0.3125″ 18 F 0.2570″ 21/64″ 11/32″ 23/64″
5/16″-24 UNF 0.3125″ 24 I 0.2720″ 21/64″ 11/32″ 23/64″
3/8″-16 UNC 0.3750″ 16 5/16″ 0.3125″ 25/64″ 13/32″ 27/64″
3/8″-24 UNF 0.3750″ 24 Q 0.3320″ 25/64″ 13/32″ 27/64″
7/16″-14 UNC 0.4375″ 14 U 0.3680″ 29/64″ 15/32″ 31/64″
7/16″-20 UNF 0.4375″ 20 25/64″ 0.3906″ 29/64″ 15/32″ 31/64″
1/2″-13 UNC 0.5000″ 13 27/64″ 0.4219″ 17/32″ 9/16″ 39/64″
1/2″-20 UNF 0.5000″ 20 29/64″ 0.4531″ 17/32″ 9/16″ 39/64″
9/16″-12 UNC 0.5625″ 12 31/64″ 0.4844″ — — —
9/16″-18 UNF 0.5625″ 18 33/64″ 0.5156″ — — —
5/8″-11 UNC 0.6250″ 11 17/32″ 0.5313″ 21/32″ 11/16″ 47/64″
5/8″-18 UNF 0.6250″ 18 37/64″ 0.5781″ 21/32″ 11/16″ 47/64″
3/4″-10 UNC 0.7500″ 10 21/32″ 0.6563″ 25/32″ 13/16″ 29/32″
3/4″-16 UNF 0.7500″ 16 11/16″ 0.6875″ 25/32″ 13/16″ 29/32″
7/8″-9 UNC 0.8750″ 9 49/64″ 0.7656″ 29/32″ 15/16″ 1-1/32″
7/8″-14 UNF 0.8750″ 14 13/16″ 0.8125″ 29/32″ 15/16″ 1-1/32″
1″-8 UNC 1.0000″ 8 7/8″ 0.8750″ 1-1/32″ 1-3/32″ 1-5/32″
1″-12 UNF 1.0000″ 12 59/64″ 0.9219″ 1-1/32″ 1-3/32″ 1-5/32″

Clearance fits marked “—” (#12, 9/16) are sizes ASME B18.2.8 does not list — omitted rather than interpolated.

ISO metric threads (coarse & fine)

Thread Major Ø Pitch Tap drill Clearance close normal loose
M1.6 × 0.35 1.6 mm 0.35 mm 1.25 mm 1.7 mm 1.8 mm 2 mm
M2 × 0.4 2 mm 0.4 mm 1.6 mm 2.2 mm 2.4 mm 2.6 mm
M2.5 × 0.45 2.5 mm 0.45 mm 2.05 mm 2.7 mm 2.9 mm 3.1 mm
M3 × 0.5 3 mm 0.5 mm 2.5 mm 3.2 mm 3.4 mm 3.6 mm
M3.5 × 0.6 3.5 mm 0.6 mm 2.9 mm 3.7 mm 3.9 mm 4.2 mm
M4 × 0.7 4 mm 0.7 mm 3.3 mm 4.3 mm 4.5 mm 4.8 mm
M5 × 0.8 5 mm 0.8 mm 4.2 mm 5.3 mm 5.5 mm 5.8 mm
M6 × 1 6 mm 1 mm 5 mm 6.4 mm 6.6 mm 7 mm
M8 × 1.25 8 mm 1.25 mm 6.8 mm 8.4 mm 9 mm 10 mm
M8 × 1 (fine) 8 mm 1 mm 7 mm 8.4 mm 9 mm 10 mm
M10 × 1.5 10 mm 1.5 mm 8.5 mm 10.5 mm 11 mm 12 mm
M10 × 1.25 (fine) 10 mm 1.25 mm 8.8 mm 10.5 mm 11 mm 12 mm
M10 × 1 (fine) 10 mm 1 mm 9 mm 10.5 mm 11 mm 12 mm
M12 × 1.75 12 mm 1.75 mm 10.2 mm 13 mm 13.5 mm 14.5 mm
M12 × 1.5 (fine) 12 mm 1.5 mm 10.5 mm 13 mm 13.5 mm 14.5 mm
M12 × 1.25 (fine) 12 mm 1.25 mm 10.8 mm 13 mm 13.5 mm 14.5 mm
M14 × 2 14 mm 2 mm 12 mm 15 mm 15.5 mm 16.5 mm
M14 × 1.5 (fine) 14 mm 1.5 mm 12.5 mm 15 mm 15.5 mm 16.5 mm
M16 × 2 16 mm 2 mm 14 mm 17 mm 17.5 mm 18.5 mm
M16 × 1.5 (fine) 16 mm 1.5 mm 14.5 mm 17 mm 17.5 mm 18.5 mm
M18 × 2.5 18 mm 2.5 mm 15.5 mm 19 mm 20 mm 21 mm
M18 × 1.5 (fine) 18 mm 1.5 mm 16.5 mm 19 mm 20 mm 21 mm
M20 × 2.5 20 mm 2.5 mm 17.5 mm 21 mm 22 mm 24 mm
M20 × 1.5 (fine) 20 mm 1.5 mm 18.5 mm 21 mm 22 mm 24 mm
M22 × 2.5 22 mm 2.5 mm 19.5 mm 23 mm 24 mm 26 mm
M24 × 3 24 mm 3 mm 21 mm 25 mm 26 mm 28 mm
Data provenance. ASME B1.1, Unified Inch Screw Threads (ASME). ISO 261 / ISO 724, ISO general purpose metric screw threads (ISO). Machinery’s Handbook — tap drill charts (Industrial Press). ASME B18.2.8, Clearance Holes for Bolts, Screws, and Studs (ASME). ISO 273, Clearance holes for bolts and screws (ISO). Tap drill recommendations assume average materials; adjust engagement for very hard or very soft stock. See all data sources.