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Clearance Hole Chart

Bolt clearance hole sizes for every metric and imperial thread, close, normal and loose fit, per ISO 273 and ASME B18.2.8.

The clearance hole is the through-hole the bolt passes through, not the tapped hole. Normal (medium) fit is the right default for almost all assembly work.

Metric coarse

Bolt	Close	Normal	Loose
M1.6×0.35	1.7 mm	1.8 mm	2 mm
M2×0.4	2.2 mm	2.4 mm	2.6 mm
M2.5×0.45	2.7 mm	2.9 mm	3.1 mm
M3×0.5	3.2 mm	3.4 mm	3.6 mm
M3.5×0.6	3.7 mm	3.9 mm	4.2 mm
M4×0.7	4.3 mm	4.5 mm	4.8 mm
M5×0.8	5.3 mm	5.5 mm	5.8 mm
M6×1	6.4 mm	6.6 mm	7 mm
M7×1	7.4 mm	7.6 mm	8 mm
M8×1.25	8.4 mm	9 mm	10 mm
M10×1.5	10.5 mm	11 mm	12 mm
M12×1.75	13 mm	13.5 mm	14.5 mm
M14×2	15 mm	15.5 mm	16.5 mm
M16×2	17 mm	17.5 mm	18.5 mm
M18×2.5	19 mm	20 mm	21 mm
M20×2.5	21 mm	22 mm	24 mm
M22×2.5	23 mm	24 mm	26 mm
M24×3	25 mm	26 mm	28 mm
M27×3	28 mm	30 mm	32 mm
M30×3.5	31 mm	33 mm	35 mm
M33×3.5	34 mm	36 mm	38 mm
M36×4	37 mm	39 mm	42 mm
M39×4	40 mm	42 mm	45 mm
M42×4.5	43 mm	45 mm	48 mm
M45×4.5	46 mm	48 mm	52 mm
M48×5	50 mm	52 mm	56 mm
M52×5	54 mm	56 mm	62 mm
M56×5.5	58 mm	62 mm	66 mm
M60×5.5	62 mm	66 mm	70 mm
M64×6	66 mm	70 mm	74 mm

Unified coarse (UNC)

Bolt	Close	Normal	Loose
#1-64 UNC	0.0810" (#46)	0.0890" (#43)	0.1040" (#37)
#2-56 UNC	0.0940" (3/32)	0.1020" (#38)	0.1160" (#32)
#3-48 UNC	0.1060" (#36)	0.1160" (#32)	0.1280" (#30)
#4-40 UNC	0.1200" (#31)	0.1280" (#30)	0.1440" (#27)
#5-40 UNC	0.1410" (9/64)	0.1560" (5/32)	0.1720" (11/64)
#6-32 UNC	0.1540" (#23)	0.1700" (#18)	0.1850" (#13)
#8-32 UNC	0.1800" (#15)	0.1900" (#9)	0.2130" (#3)
#10-24 UNC	0.2060" (#5)	0.2210" (#2)	0.2380" (B)
#12-24 UNC	0.2340" (A)	0.2460" (D)	0.2656" (17/64)
1/4-20 UNC	0.2660" (17/64)	0.2810" (9/32)	0.2970" (19/64)
5/16-18 UNC	0.3280" (21/64)	0.3440" (11/32)	0.3590" (23/64)
3/8-16 UNC	0.3910" (25/64)	0.4060" (13/32)	0.4220" (27/64)
7/16-14 UNC	0.4530" (29/64)	0.4690" (15/32)	0.4840" (31/64)
1/2-13 UNC	0.5310" (17/32)	0.5620" (9/16)	0.6090" (39/64)
9/16-12 UNC	0.5940" (19/32)	0.6250" (5/8)	0.6720" (43/64)
5/8-11 UNC	0.6560" (21/32)	0.6880" (11/16)	0.7340" (47/64)
3/4-10 UNC	0.7810" (25/32)	0.8120" (13/16)	0.9060" (29/32)
7/8-9 UNC	0.9060" (29/32)	0.9380" (15/16)	1.0310" (1-1/32)
1-8 UNC	1.0310" (1-1/32)	1.0940" (1-3/32)	1.1560" (1-5/32)
1-1/8-7 UNC	1.1560" (1-5/32)	1.2190" (1-7/32)	1.3120" (1-5/16)
1-1/4-7 UNC	1.2810" (1-9/32)	1.3440" (1-11/32)	1.4380" (1-7/16)
1-3/8-6 UNC	1.4380" (1-7/16)	1.5000" (1-1/2)	1.6090" (1-39/64)
1-1/2-6 UNC	1.5620" (1-9/16)	1.6250" (1-5/8)	1.7340" (1-47/64)