Hole size and fastener reference

Clearance Hole Size Chart for Bolts and Screws (Imperial)

Q: How should I use this hole size chart?

Use it for quick fastener hole sizing, drawing checks, and machining setup planning.

Q: What is the difference between close, normal, and loose fit?

Close fits provide better location control, normal fits suit typical assembly, and loose fits give more clearance for alignment or tolerance stack-up.

Q: Can this chart replace the fastener standard?

No. Use it as a fast reference; final hole dimensions should follow the current standard, drawing notes, tolerance requirements, and manufacturing process.

Search Clearance Hole Size Chart for Bolts and Screws (Imperial) for quick fastener hole sizing, drawing checks, machining setup, and design review.

Fastener hole reference

Search Clearance Hole Size Chart for Bolts and Screws (Imperial)

Filter the chart by fastener size, hole diameter, fit class, counterbore diameter, countersink size, or depth.

Clearance Holes

Hole fit

Pick the fit first

Choose close, normal, loose, or free fit based on assembly tolerance and location needs.

Machining check

Check head clearance

Use counterbore or countersink dimensions to confirm the screw head seats as intended.

Reference table

Clearance hole chart - Imperial

Screw Size	Close Fit		Free Fit
Screw Size	Drill Size	Decimal Equivalent	Drill Size	Decimal Equivalent
0	52	0.0635	50	0.0700
1	48	0.0760	46	0.0810
2	43	0.0890	41	0.0960
3	37	0.1040	35	0.1100
4	32	0.1160	30	0.1285
5	30	0.1285	29	0.1360
6	27	0.1440	25	0.1495
8	18	0.1695	16	0.1770
10	9	0.1960	7	0.2010
12	2	0.2210	1	0.2280
14	D	0.2460	F	0.2570
1/4	F	0.2570	H	0.2660
5/16	P	0.3230	Q	0.3320
3/8	W	0.3860	X	0.3970
7/16	29/64	0.4531	15/32	0.4687
1/2	33/64	0.5156	17/32	0.5312

How to use

Practical checks for fastener holes

Clearance

C = D_hole - D_fastener

Positive clearance gives assembly room between the fastener shank and the hole.

Counterbore depth

depth ≥ head height + allowance

Counterbore depth should seat the head with the required flush, recessed, or proud condition.

Countersink diameter

D = d + 2h tan(θ/2)

Countersink diameter depends on screw head diameter, depth, and included angle.

Fit selection

close < normal < loose

Tighter fits improve location control; looser fits improve assembly tolerance and speed.

Definitions

What the hole size values mean

Pilot Hole

The through hole for the screw or bolt shank before counterboring or countersinking.

Counterbore Diameter

The flat-bottom recess diameter used to seat a cylindrical screw head or washer face.

Counterbore Depth

The recess depth that controls whether the fastener head sits flush, below, or above the surface.

Countersink Angle

The included cone angle used for flat head screws and countersunk fasteners.

FAQ