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Reference Chart

Countersink Size Chart

Find body drill, countersink diameter, angle, and pilot hole for flat head screws from #2 to 1/2". Covers both 82° and 90° countersinks.

Screw Size ▲	Head Type ▲	Body Drill (in) ▲	Countersink Dia (in) ▲	Countersink Angle ▲	Pilot Hole (in) ▲
#2	Flat Head	0.089	0.197	82°	0.073
#4	Flat Head	0.116	0.225	82°	0.089
#6	Flat Head	0.144	0.279	82°	0.104
#8	Flat Head	0.170	0.322	82°	0.125
#10	Flat Head	0.196	0.373	82°	0.141
#12	Flat Head	0.221	0.420	82°	0.166
1/4"	Flat Head	0.257	0.477	82°	0.196
5/16"	Flat Head	0.323	0.567	82°	0.252
3/8"	Flat Head	0.386	0.682	82°	0.302
7/16"	Flat Head	0.453	0.788	82°	0.368
1/2"	Flat Head	0.520	0.894	82°	0.422
#2	Flat Head	0.089	0.185	90°	0.073
#4	Flat Head	0.116	0.212	90°	0.089
#6	Flat Head	0.144	0.263	90°	0.104
#8	Flat Head	0.170	0.305	90°	0.125
#10	Flat Head	0.196	0.352	90°	0.141
#12	Flat Head	0.221	0.398	90°	0.166
1/4"	Flat Head	0.257	0.452	90°	0.196
5/16"	Flat Head	0.323	0.538	90°	0.252
3/8"	Flat Head	0.386	0.648	90°	0.302
7/16"	Flat Head	0.453	0.750	90°	0.368
1/2"	Flat Head	0.520	0.851	90°	0.422

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Notes on This Chart

82° is standard for ANSI inch flat head screws. 90° is standard for ISO metric flat head screws.
Countersink diameter matches the screw head outer diameter for a flush fit.
Pilot hole sizes are for hardwood and metal. Use larger pilots for softwood.
Always test-fit on scrap material before running production parts.

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Frequently Asked Questions

What is the difference between 82 and 90 degree countersinks?

82 degrees is the standard angle for inch flat head screws (ANSI). 90 degrees is the standard for metric flat head screws (ISO). Using the wrong angle leaves gaps around the screw head.

How deep should I countersink?

Countersink until the screw head sits flush with the surface. The countersink diameter in the chart matches the head diameter. Go slightly deeper if you want the head below the surface.

What is a body drill vs. a pilot hole?

The body drill matches the screw body diameter. It lets the screw pass through the top piece freely. The pilot hole is smaller and goes into the bottom piece. It guides the screw threads.

Can I countersink on a CNC mill?

Yes. Use a single-flute or multi-flute countersink cutter. Program the Z depth to match the head diameter. Use a slow feed rate for a clean finish. Chamfer mills also work well for CNC countersinking.

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