Countersunk Hole Treatment

Countersunk Holes

A countersink is a tapered hole drilled with a wide outer portion. A common usage of the countersunk hole is to allow the head of a flat head bolt or screw, when placed in the hole, to sit flush with or below the surface of the surrounding material. A Countersunk Hole is made with use of a drill bit and treating a laser cut hole with the bit to taper out the countersink.

Unless otherwise specified, countersunk holes are of a diameter 0.10-.015" larger than the basic size of the laser hole at . 80 (or 82) degree and 100 degree countersinks are most common for flat head screws.

Proper hole size and countersink size for screws.

Table for 82 Degree Countersink

Screw Size	#4	#5	#6	#8	#10	#12	1/4-20
Max Head Diameter	0.225	0.252	0.279	0.332	0.385	0.438	0.507
Min Head Diameter	0.207	0.232	0.257	0.308	0.359	0.410	0.477
Top Ctsk Diameter	0.216	0.242	0.268	0.320	0.372	0.424	0.492
Body Diameter	0.112	0.125	0.138	0.164	0.190	0.216	0.250

Hole Sizes Before Countersunk for 82 degree Screws (+/- .005)

Screw Size Thickness	#4	#5	#6	#8	#10	#12	1/4-20
0.020	0.1950	0.2220	0.2490	0.3020	0.3550	0.4060	0.4770
0.025	0.1870	0.2130	0.2400	0.2930	0.3460	0.4060	0.4680
0.030	0.1760	0.2010	0.2280	0.2810	0.3340	0.4060	0.4560
0.035	0.1660	0.1960	0.2210	0.2740	0.3280	0.4060	0.4490
0.042	0.1600	0.1870	0.2130	0.2630	0.3170	0.4060	0.4370
0.050	0.1410	0.1700	0.1960	0.2500	0.3030	0.3830	0.4060
0.060	0.1280	0.1520	0.1790	0.2320	0.2850	0.3830	0.4060
0.074	0.1250	0.1280	0.1560	0.2080	0.2630	0.3680	0.3830
0.090	0.1250	0.1280	0.1560	0.1940	0.2500	0.3360	0.3680
0.120	0.1250	0.1280	0.1560	0.1870	0.2130	0.3030	0.3120
0.179	0.1250	0.1280	0.1560	0.1870	0.2130	0.2320	0.3120
0.250	0.1250	0.1280	0.1560	0.1870	0.2130	0.2320	0.3120

Table for 100 Degree Countersink

Screw Size	#4	#5	#6	#8	#10	#12	1/4-20
Max Head Diameter	0.231	0.257	0.283	0.335	0.387	0.439	0.507
Min Head Diameter	0.201	0.227	0.253	0.305	0.357	0.409	0.477
Top Ctsk Diameter	0.216	0.242	0.268	0.320	0.372	0.424	0.492
Body Diameter	0.112	0.125	0.138	0.164	0.190	0.216	0.250

Hole Sizes Before Countersunk for 100 degree Screws (+/- .005)

Screw Size Thickness	#4	#5	#6	#8	#10	#12	1/4-20
0.020	0.1870	0.2130	0.2490	0.3020	0.3460	0.4060	0.4770
0.025	0.1870	0.2130	0.2320	0.2930	0.3460	0.4060	0.4680
0.030	0.1760	0.1960	0.2210	0.2740	0.3360	0.3830	0.4560
0.035	0.1600	0.1870	0.2130	0.2630	0.3120	0.3680	0.4370
0.042	0.1410	0.1760	0.2960	0.2500	0.3130	0.4680	0.4240
0.050	0.1250	0.1280	0.1760	0.2320	0.2850	0.3360	0.4640
0.060	0.1250	0.1280	0.1560	0.2130	0.2850	0.3830	0.4060
0.074	0.1250	0.1280	0.1560	0.1870	0.2130	0.2320	0.3120
0.090	0.1250	0.1280	0.1560	0.1870	0.2130	0.2320	0.3120
0.120	0.1250	0.1280	0.1560	0.1870	0.2130	0.2320	0.3120
0.179	0.1250	0.1280	0.1560	0.1870	0.2130	0.2320	0.3120
0.250	0.1250	0.1280	0.1560	0.1870	0.2130	0.2320	0.3120