Hole size and fastener reference

Countersunk Hole Size Chart for Socket Flat Head Screws (ANSI Metric)

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 Countersunk Hole Size Chart for Socket Flat Head Screws (ANSI Metric) for quick fastener hole sizing, drawing checks, machining setup, and design review.

Fastener hole reference

Search Countersunk Hole Size Chart for Socket Flat Head Screws (ANSI Metric)

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

Countersinks

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

Countersunk hole chart - ANSI Metric

Fastener Size (Thread)	Pilot Hole Diameter (mm)			Countersink Diameter (mm)	Countersink Angle (°)
Fastener Size (Thread)	Close Fit H12	Normal Fit H13	Loose Fit H14	Countersink Diameter (mm)	Countersink Angle (°)
M3	3.2	3.4	3.6	6.94	90
M3.5	3.7	3.9	4.2	6.94	90
M4	4.3	4.5	4.8	9.18	90
M5	5.3	5.5	5.8	11.47	90
M6	6.4	6.6	7	13.71	90
M8	8.4	9	10	18.25	90
M10	10.5	11	12	22.73	90
M12	13	13.5	14.5	27.21	90
M16	17	17.5	18.5	33.99	90
M20	21	22	24	40.71	90
M24	25	26	28	41	90

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