Flat Head Socket Screws
Flat head socket screws have a countersunk head that finishes flush with a hex socket drive. Inch and metric heads have different countersink angles.
Countersink angle
| Series | Head angle | Standard |
|---|---|---|
| Inch | 82 degrees | ASME B18.3 |
| Metric | 90 degrees | ISO 10642 / DIN 7991 |
These tables carry the same figures as the printed sheet below.
The printed sheet
See an error on this sheet?
Tell us what is wrong.
Text version of this sheet
ISO 10642 / DIN 7991 · ASME B18.3 · flat head socket screws
What it is
FIELD IDENTIFICATION
Flat head socket screws have a countersunk head that finishes flush with a hex socket drive. Inch and
metric heads have different countersink angles.
Countersunk head sits flush, hex socket drive
Countersink angle
Series
Head angle
Standard
Inch
82 degrees
ASME B18.3
Metric
90 degrees
ISO 10642 / DIN 7991
Key points
An 82-degree screw in a 90-degree countersink (or the reverse) bears on a line, not a cone, and can crack the head or loosen.
Length is measured overall, from the top of the head.
Governing standards: ISO 10642; ASME B18.3-2012; ASTM F835-23. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard
always take precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-24F3E2 · thefastenerapp.com/fastener-guide/technical-reference/flat-head-socket-screws · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
