Size picker · Hex head · ASME B18.2.1
UNC and UNF hexagon set screw sizes.
Threaded full length, hex head, imperial thread — the everyday inch fastener on older plant, agricultural kit and anything American. Pick a size and length for the spanner size and head height, and pick UNC or UNF, because the diameter alone does not tell you the thread.
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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Job stopped? Ring 01327 877577 and we'll check the stock while you're on.
Read the full ASME B18.2.1 size chart
| Size | 3/8" | 1/2" | 5/8" | 3/4" | 7/8" | 1" | 1 1/4" | 1 1/2" | 1 3/4" | 2" | 2 1/4" | 2 1/2" | 2 3/4" | 3" | 3 1/4" | 3 1/2" | 3 3/4" | 4" | 4 1/4" | 4 1/2" | 5" | 5 1/2" | 5 3/4" | 6" | 6 1/2" | 7" | 9" | 9 1/2" | 10" | 10 1/2" |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1/4 | ||||||||||||||||||||||||||||||
| 5/16 | ||||||||||||||||||||||||||||||
| 3/8 | ||||||||||||||||||||||||||||||
| 7/16 | ||||||||||||||||||||||||||||||
| 1/2 | ||||||||||||||||||||||||||||||
| 9/16 | ||||||||||||||||||||||||||||||
| 5/8 | ||||||||||||||||||||||||||||||
| 3/4 | ||||||||||||||||||||||||||||||
| 7/8 | ||||||||||||||||||||||||||||||
| 1 |
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.
Set screw, bolt, or cap screw?
In the UK trade a set screw is threaded all the way to the head; a bolt has a plain shank under it. Everything on this chart is fully threaded. The American standard calls the same part a hex cap screw, which is worth knowing when you are reading a US parts list — it is not a socket grub screw, which is what "set screw" means in the States.
The spanner size follows the standard, not the diameter: a 1/2 inch set screw takes a 3/4 inch AF spanner. Imperial spanners are marked across the flats, so the number on the spanner is the figure in the s row of the table, not the thread size.
UNC or UNF
Most imperial diameters exist in both. A 1/2 inch is 13 threads per inch coarse and 20 fine. They will not interchange, and a mismatched pair strips a thread rather than announcing itself, so count the threads or bring the old one in. Coarse is the general-purpose choice and what most of our stock is.
Where these figures come from
Width across flats and head height are ASME B18.2.1, read from the published standard and cross-checked against a second independent table before printing. The lengths on the chart come from what our own book and our five fastener suppliers actually list — not from a preferred series — so a length shown is a length someone stocks.
We hold the common sizes in bright zinc and self-colour high-tensile. Stainless, longer lengths and the BSW/BSF Whitworth range are available to order — ask us.
Working in metric instead?
See the metric hex setscrew sizes chart for DIN 933, or the UNC and UNF socket cap screw chart for an internal hex drive.
Not sure which you need?
Bring the old one in, or send us a photo. We are on Baird Close in Daventry and we still keep imperial hex on the shelf.
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.