Short Run Pro | Helpful Resources on Countersinking

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Countersinking Sizes

Countersinks

A countersink is a tapered hole drilled with a wide outer portion. A common usage is to allow the head of a countersunk bolt or screw, when placed in the hole, to sit flush with or below the surface of the surrounding material.

Unless otherwise specified, countersink to a diameter 0.10-.015" larger than the basic size of the thread. 80 (or 82) degree and 100 degree counter sinks 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 Dia.	0.225	0.252	0.279	0.332	0.385	0.438	0.507
Min Head Dia.	0.207	0.232	0.257	0.308	0.359	0.410	0.477
Top Ctsk Dia.	0.216	0.242	0.268	0.320	0.372	0.424	0.492
Body Dia.	0.112	0.125	0.138	0.164	0.190	0.216	0.250

Hole sizes before countersinking for 82 degree Screws (+/- .005)

Screw Size	#4	#5	#6	#8	#10	#12	1/4-20
Thickness
0.020	0.1950	0.2220	0.2490	0.3020	0.3550	0.4060	0.4770
.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	0.4240
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 Dia.	0.231	0.257	0.283	0.335	0.387	0.439	0.507
Min Head Dia.	0.201	0.227	0.253	0.305	0.357	0.409	0.477
Top Ctsk Dia.	0.216	0.242	0.268	0.320	0.372	0.424	0.492
Body Dia.	0.112	0.125	0.138	0.164	0.190	0.216	0.250

Hole sizes before countersinking for 100 degree Screws (+/- .005)

Screw Size	#4	#5	#6	#8	#10	#12	1/4-20
Thickness
0.020	0.1870	0.2130	0.2490	0.3020	0.3460	0.4060	0.4770
.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	0.312	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