Help with size of bolts, please

[GB]

We inherited a cot with only half the bolts. It's this one:

We have the 65mm bolts, but the 50mm ones are missing. The leaflet specifies the length of the bolts, but not the diameter or thread.

I checked the diameter of the bolts we do have, with a micrometer gauge, and they have an outside diameter of 6.27 mm (as closely as I can get it). That is the outside diameter of the threaded part.

What size is that? It seems too big for M6?

The 65mm ones do seem to fit the nuts intended for the 50mm bolts, btw.

[Alan J. Wylie]

1/4" = 6.25mm

[Alan J. Wylie]

Ooops, finger trouble in the cold. 6.35mm

[Alan J. Wylie]

[Colin Bignell]

While I agree, after the typo has been corrected, it does seem odd for what, from dates in the instructions, appears to be of relatively modern manufacture and where all measurements are given in millimetres. If it is an American import, I suspect they could be 1/4" UNF.

[Clive Arthur]

I was surprised when I bought a towel rail from China via eBay to find that the Allen grub screws were not metric. I suppose if a manufacturer can find a whole load of screws cheap, then it doesn't matter what size standard they comply or complied with.

[Roger Mills]

Can you measure the thread pitch - as in how many threads per inch or whatever? That will help to identify what the tread is. The diameter alone is not sufficient. There are lots of cases where there are 2 or more bolts with the diameter but different pitches.

[Joe]

Does the OP have a camera (video, film or still) of any kind? The mounting hole will be 1/4-20 UNF. That is also remarkably close to 1/4" Whitworth, I believe there's only a small difference in thread angle between them, and they are interchangeable.

[Roger Mills]

Not quite right. 1/4" Whitworth is very similar to 1/4" UNC - (Not UNF) Both Whitworth (BSW) and UNC are coarse threads, and the 1/4" variety both have 20 threads per inch (TPI)

The fine thread equivalents - BSF and UNF are less similar, with different pitches. 1/4" BSF is 26 TPI and 1/4" UNF is 28 TPI.

6mm metric bolts have a diameter only slightly less than 1/4". The coarse thread variety has a pitch of 1mm (25.4 TPI) and the fine variety has a pitch of 0.75mm (33.9 TPI)

So the OP has quite a lot to choose from - hence my suggestion about measuring the pitch.

[Paul]

The thread could be 1/4 20TPI.

The Everbilt dowel nut has a Philips head instead of a Slot head like this one.

Some samples of "connector bolts", are at the bottom of the page. Those would be the mates for the item, presumably.

Paul