Size charts · Socket screws
Socket screw sizes.
Everything driven by a hex key. Pick a diameter and a length and see it drawn to scale, with the head diameter, the head height, the key size and the engagement depth — the four figures that decide whether it fits the counterbore and whether the key will hold it.
SZ-03 / DWS·DAVENTRY
Socket cap screw sizes
The machine-build workhorse, DIN 912. Head diameter, head height and the Allen key it takes, for every size from M2 to M30 — drawn as you pick it.
M2 – M30 · DIN 912 · 12.9 / 10.9 / 8.8 / A2 / A4
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SZ-04 / DWS·DAVENTRY
Low head cap screw sizes
Half the head height of a DIN 912, for shallow counterbores — and a smaller key than the cap screw of the same thread, which catches people out. DIN 7984.
M3 – M24 · DIN 7984 · Smaller key size
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SZ-05 / DWS·DAVENTRY
Button head screw sizes
Low domed head, internal hex, ISO 7380-1. Wide bearing face and nothing sharp to catch — with the strength trade-off spelled out.
M3 – M16 · ISO 7380-1 · 10.9 / A2 / A4
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SZ-06 / DWS·DAVENTRY
Flanged button head sizes
A button head with the washer built in, ISO 7380-2. Head and flange diameters both given — the flange is what sits against the work.
M3 – M12 · ISO 7380-2 · Flange diameter
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SZ-07 / DWS·DAVENTRY
Countersunk socket screw sizes
Flush-finishing 90° heads, DIN 7991 — and a warning worth reading before you order M22 or M24, because the standard switches to a 60° head.
M3 – M24 · DIN 7991 · 90° · 60° over M20
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SZ-08 / DWS·DAVENTRY
Grub screw sizes
All five points — cup, flat, cone, dog and knurled cup — with what each one actually does to the shaft, plus key sizes and point dimensions.
M2 – M24 · DIN 913 / 914 / 915 / 916 · 45H
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SZ-09 / DWS·DAVENTRY
UNC & UNF socket cap screw sizes
The imperial cap screw, #0 to 2 inch. Head diameter, head height and the Allen key — and pick the thread, because most sizes come in both coarse and fine.
#0 – 2" · ASME B18.3 · UNC / UNF · 12.9 / A2
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SZ-13 / DWS·DAVENTRY
UNC & UNF countersunk socket sizes
The inch flat head is 82°, not the metric 90° — seat one in the wrong countersink and it bears on its rim. Head diameter, socket size and lengths.
#2 – 1/2" · ASME B18.3 · 82° · UNC / UNF
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SZ-14 / DWS·DAVENTRY
UNC & UNF button head sizes
The inch button head — the low-domed finish screw. Head diameter, height and socket size, in the slice of the range the trade actually lists.
#6 – 5/16" · ASME B18.3 · UNC / UNF
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SZ-15 / DWS·DAVENTRY
UNC & UNF grub screw sizes
What an American parts list calls a socket set screw. Cup point — the one the shelf holds — with the hex key size, which is not a metric key.
#2 – 1/2" · ASME B18.3 · cup point · UNC / UNF
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The head form is the whole decision
Side on, a cap head and a low head look nearly the same, and that is exactly where the mistakes happen. A cap head stands about as tall as the thread is wide; a low head is roughly half that, for when the counterbore is shallow. A countersunk sits flush and needs a 90° seat — check the angle, because some are cut at 60° and will not seat in a 90° countersink. A button is decorative and low, and a flanged button spreads the load so you can leave the washer out.
⚠️ Button, low head, flanged and countersunk socket screws are rated at about 80% of their property class — the standards say so in their own scope lines, because the shallow head and socket govern rather than the thread. Size the joint on that, not on the class stamped on the head.
Not sure which you need?
Bring the old one in, or send us a photo. We are on Baird Close in Daventry with metric and imperial stock across the common classes and finishes.
More size charts
Every size, drawn to scale.
Hex setscrews
DIN 933 · full thread
Hex bolts
DIN 931 · part thread
Socket cap screws
DIN 912
Low head cap screws
DIN 7984
Button head screws
ISO 7380-1
Flanged button heads
ISO 7380-2
Countersunk socket screws
DIN 7991
Grub screws
DIN 913–916 · five points
Nuts
DIN 934 · nyloc · thin · Stover · flange
Washers
ISO 7089 · BS 4320 · penny
Not sure what the markings on the head mean? Bolt grades explained covers 8.8, 10.9, 12.9, stainless A2 and A4, and the imperial SAE grades.
All of it comes off the shelf at Baird Close — see the full fasteners & fixings range, or every size guide.