Size picker · Button head · ASME B18.3
UNC and UNF button head screw sizes.
The inch button head — the low-domed finish screw. Pick a size and length for the head diameter, height and socket size, and pick UNC or UNF.
1 Pick a diameter
2 Pick a length
Choose a diameter first.
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Drawn to proportion from the standard dimensions. Illustration, not a photograph of the item.
Selected
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| Sym | Dimension | Value |
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Job stopped? Ring 01327 877577 and we'll check the stock while you're on.
Read the full ASME B18.3 size chart
| Size | 3/16" | 1/4" | 3/8" | 1/2" | 5/8" | 3/4" | 1" | 1 1/4" | 1 1/2" | 1 3/4" | 2" | 3" |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| #6 | ||||||||||||
| #8 | ||||||||||||
| #10 | ||||||||||||
| 1/4 | ||||||||||||
| 5/16 |
The range shown is what fastener wholesalers commonly list — not a claim about what the standard mandates, and not a stock list. In-between lengths (85, 95, 170…), lengths past 300mm and odd diameters like M7 are made too, and availability varies by finish and grade — ask us for anything you can't see.
A finish screw, not a structural one
The shallow head means a shallow socket, and the standard itself says buttons are not for high-strength joints — the socket rounds before a deep-socket cap screw would let go. Where the load matters, use a UNC/UNF cap screw and live with the taller head.
The range stops at 5/8 by design
ASME B18.3 buttons run #0 to 5/8 inch and no further — a bigger button is not a standard part. What is on this chart is the slice of that range the suppliers actually list; the small gauge sizes and anything odd are to order.
Where these figures come from
Head diameter, height and socket size are ASME B18.3, read from two independent published tables that agree to the thousandth. Lengths are what our suppliers actually list. Buttons come threaded to the head.
Working in metric instead?
See the metric button head chart for ISO 7380-1.
Not sure which you need?
Bring the old one in, or send us a photo. We are on Baird Close in Daventry.
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.