Countersink Size Chart — 82° and 90° Flat-Head Screws

Countersink size lookup

Use the chart to compare the fastener family, included angle, clearance-hole reference, head diameter, countersink diameter, and depth. Search for a size such as M4, M6, #10, or 1/4 in. Metric rows use millimetres. The inch family keeps its source inch values in the row notes and also shows canonical millimetre values for consistent comparison.

MECHANITEC / ENGINEERING REFERENCE

Countersink Size Chart — Metric 90° and Inch 82°

A bounded reference for ISO metric countersinks and one 82° inch flat-head socket-cap family, with source values separated from calculated cone depth.

1–18 of 18 matching rows (18 total)

Countersink Size Chart — Metric 90° and Inch 82° — page 1 of 1
System	Fastener designation	Fastener family	Included angle (deg)	Clearance-hole reference (mm)	Head major diameter (mm)	Target countersink major diameter (mm)	Source/nominal depth (mm)	Calculated cone depth (mm)	Source clearance value	Source head value	Source depth/height	Governing source	Value status
metric	M1.6	ISO 15065 / ISO 7721 countersunk head geometry	90	1.8	3.7	3.7	0.95	0.95	1.80–1.94 mm dh	3.60–3.70 mm Dc	t ≈ 0.95 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M2	ISO 15065 / ISO 7721 countersunk head geometry	90	2.4	4.5	4.5	1.05	1.05	2.40–2.54 mm dh	4.40–4.50 mm Dc	t ≈ 1.05 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M2.5	ISO 15065 / ISO 7721 countersunk head geometry	90	2.9	5.6	5.6	1.35	1.35	2.90–3.04 mm dh	5.50–5.60 mm Dc	t ≈ 1.35 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M3	ISO 15065 / ISO 7721 countersunk head geometry	90	3.4	6.5	6.5	1.55	1.55	3.40–3.58 mm dh	6.30–6.50 mm Dc	t ≈ 1.55 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M3.5	ISO 15065 / ISO 7721 countersunk head geometry	90	3.9	8.4	8.4	2.25	2.25	3.90–4.08 mm dh	8.20–8.40 mm Dc	t ≈ 2.25 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M4	ISO 15065 / ISO 7721 countersunk head geometry	90	4.5	9.6	9.6	2.55	2.55	4.50–4.68 mm dh	9.40–9.60 mm Dc	t ≈ 2.55 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M5	ISO 15065 / ISO 7721 countersunk head geometry	90	5.5	10.65	10.65	2.58	2.575	5.50–5.68 mm dh	10.40–10.65 mm Dc	t ≈ 2.58 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M6	ISO 15065 / ISO 7721 countersunk head geometry	90	6.6	12.85	12.85	3.13	3.125	6.60–6.82 mm dh	12.60–12.85 mm Dc	t ≈ 3.13 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M8	ISO 15065 / ISO 7721 countersunk head geometry	90	9	17.55	17.55	4.28	4.275	9.00–9.22 mm dh	17.30–17.55 mm Dc	t ≈ 4.28 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
metric	M10	ISO 15065 / ISO 7721 countersunk head geometry	90	11	20.3	20.3	4.65	4.65	11.00–11.27 mm dh	20.00–20.30 mm Dc	t ≈ 4.65 mm	ISO 15065:2005 with ISO 7721:1983	Source ranges and approximate depth; calculated depth uses lower dh and upper Dc.
inch	#4-40	ASME B18.3.2 82° flat-head socket cap screw	82	2.946	6.477	6.477		2.031	0.116 in body drill	0.255 / 0.218 in A sharp max / abs min	H = 0.083 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.
inch	#6-32	ASME B18.3.2 82° flat-head socket cap screw	82	3.658	7.798	7.798		2.381	0.144 in body drill	0.307 / 0.263 in A sharp max / abs min	H = 0.097 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.
inch	#8-32	ASME B18.3.2 82° flat-head socket cap screw	82	4.318	9.119	9.119		2.761	0.170 in body drill	0.359 / 0.311 in A sharp max / abs min	H = 0.112 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.
inch	#10-24	ASME B18.3.2 82° flat-head socket cap screw	82	4.978	10.439	10.439		3.141	0.196 in body drill	0.411 / 0.359 in A sharp max / abs min	H = 0.127 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.
inch	1/4-20	ASME B18.3.2 82° flat-head socket cap screw	82	6.528	13.487	13.487		4.003	0.257 in body drill	0.531 / 0.480 in A sharp max / abs min	H = 0.161 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.
inch	5/16-18	ASME B18.3.2 82° flat-head socket cap screw	82	8.204	16.662	16.662		4.865	0.323 in body drill	0.656 / 0.600 in A sharp max / abs min	H = 0.198 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.
inch	3/8-16	ASME B18.3.2 82° flat-head socket cap screw	82	9.804	19.837	19.837		5.771	0.386 in body drill	0.781 / 0.720 in A sharp max / abs min	H = 0.234 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.
inch	1/2-13	ASME B18.3.2 82° flat-head socket cap screw	82	13.208	23.825	23.825		6.107	0.520 in body drill	0.938 / 0.872 in A sharp max / abs min	H = 0.251 in reference	ASME B18.3.2 manufacturer reference; body drill cross-check RivCut	Head/angle sourced; inch-to-mm converted; cone depth calculated.

Search and sort apply to all 18 rows. Print and CSV include only the 18 rows shown on this page.

Choose the row for the exact head style and standard. A flat-head socket screw, a slotted machine screw, an oval-head screw, and a rivet can use different head dimensions even when the thread or body diameter looks similar.

82° versus 90°

The included angle is the angle across the cone, not the angle from the surface to one side. The 82° inch family in this chart is separated from the 90° metric family because the same major and minor diameters produce different depths at different angles. A cutter with the wrong angle can leave a ring, contact the head at the wrong location, or remove more material than the drawing allows.

For metric general-purpose countersinks, ISO 15065:2005 specifies the countersink dimensions for head configurations governed by ISO 7721:1983. The ISO table supplies clearance-hole limits, countersink major-diameter limits, and an approximate depth. These are source values for the metric rows, not values inferred from a generic 90° rule.

The 82° inch rows are a bounded flat-head socket cap screw family. The head dimensions are tied to the cited ASME B18.3 manufacturer reference, and the body-drill values are shown as a separate reference input. Confirm the exact screw series, drive style, material, and supplier before releasing a production drawing.

How to calculate countersink depth

When the minor diameter and target major diameter are known, use the named countersink-depth-v1 formula:

depth = (target major diameter − minor diameter) ÷ (2 × tan(included angle ÷ 2))

Use matching units for every diameter. For example, an 82° row with a 0.196 in body drill and a 0.411 in target major diameter gives a geometric depth of about 0.123 in. An ISO M4 row using a 4.50 mm clearance-hole minimum and a 9.60 mm countersink maximum gives 2.55 mm at 90°. The chart records those results as calculated so you can distinguish them from a standard’s published approximate depth.

The formula describes the ideal cone. The real feature may need an allowance for edge break, coating, burrs, tool runout, surface finish, or a slightly recessed head. Dimension the major diameter and angle on the drawing when the fit matters, and verify the result with the actual screw rather than relying only on a drill scale.

Use the clearance hole as a separate decision

The countersink does not decide the through-hole size. The clearance hole must let the screw shank pass through the upper part without binding, while the threaded part below may require a different pilot or tap-drill choice. Use the clearance hole size chart for a broader metric and inch hole lookup. If you need a cutter designation, compare it with the drill bit size chart.

Do not confuse a body drill with a pilot hole. A body drill clears the screw in the top part. A pilot hole guides threads in the mating part. If you are making a tapped hole, use the tap drill size chart and the tap manufacturer’s guidance for the material and engagement.

Metric hex-socket screws and ISO 10642

Metric hexagon socket countersunk screws are a distinct fastener family. The current standard is ISO 10642:2026, which covers reduced-loadability hexagon socket countersunk head screws from M2 to M20. Use ISO 10642:2026 and the exact screw’s product dimensions when that family controls the assembly; do not assume that every metric flat-head screw has the same head or socket geometry.

Countersink versus counterbore

A countersink has a conical wall and normally seats a flat head. A counterbore has a cylindrical wall and a flat shoulder for a socket-head cap screw. Do not substitute one feature for the other. For the cylindrical recess, use the counterbore size chart and keep the head-clearance allowance separate from the fastener’s sourced dimensions.

What this chart does not cover

100° is out of scope here. Some aerospace, structural, and other special fastener families use 100° heads, but their head dimensions, gaging rules, materials, and installation requirements are family-specific. Do not select a 100° cutter from this chart. Obtain the current governing fastener and hole standard before adding that family.

SOLIDWORKS Hole Wizard can model a countersunk feature after you select the correct standard and dimensions. Treat the CAD feature as a representation of the engineering decision, then confirm the final callout, angle, diameter, depth, material thickness, and edge distance on the drawing. The SOLIDWORKS Hole Wizard guide covers the modeling workflow.

Frequently asked questions

What angle should I use for a metric flat-head screw?

Use the angle required by the exact product standard. The ISO 15065/ISO 7721 geometry represented here is 90°. Confirm the product family before machining.

What angle should I use for an inch flat-head screw?

The bounded inch family in this chart uses 82°. Other inch and aerospace families can differ, so check the fastener specification instead of assuming that every flat head is 82°.

How deep should a countersink be?

Start with the included-angle formula and the actual minor and major diameters. Then test-fit the exact fastener and account for tolerances, edge break, finish, and the required flush or recessed condition.