Odd sized Allen bolts?

The message from alan@darkroom.+.com (A.Lee) contains these words:

Can you see it well enough to be sure it's an Allen socket? Small hex sockets don't work too well and it may be a spline/Torx bit instead.

I think you may be slightly confused. There are only two ranges of hexagon keys. An imperial range, and a metric range. The sizes of hex keys are all measured in terms of AF (Across Flats) Not by the screw or bolt size. Hence a 1/4" hex key, or an 8mm hex key.

You give no hint of the size you might be needing, but IME there are few non-preferred sizes in hex key sets, 7mm is the only size that comes to mind, so unless it's a real oddball size, the chances are that a suitable key will be found in any decent set of keys. Either metric or imperial.

Try an autofactor, or small tool stockist, if Halfords don't have one. Mike.

Yes, defintely an allen head, a 2.5mm key was too big(or could it have been a 2mm,I'm not sure), then the next size up, 3mm was too big, so I went and got out the imperial set, there was one that was a close fit, but it was still a little too small to get a grip. I've also got a box of odds and ends allen keys, none of these were close either. I thought the key may have been worn around the edges, so I even went out and bought a new imperial set, and it was still a little too small. Do electrical parts have their own allen head sizes? I know for occasional nuts I have to use a BA spanner, but I've never come across an odd allen bolt size before. Ta Alan.

See my other post. I have 2 decent sets of keys, MM and AF, none of these would fit the bolt in question.It is between 2 and 3mm head size.I cant remember which it was, but IIRC, the 2.5mm was too small, and the

3mm too big, imperial keys were similar. I suppose there is a chance that the bolt is worn inside, hence will not grip, it was getting close to 16:30 when I was doing this, and really wanted to get home, so I didnt bother changing it, and left the noisy old one in situ until I can find a key to fit, or take a replacement gear to fit in place of the old one. Alan.

They do a nice multi set in Wicks for a tenner, in a plastic case, with around 40 allen keys of mixed sizes (20 x imp, 20 x metric). Look for a open black case sealed in a plastic seethrough pack, the case folds into a closed holder when released from the plastic.

PDH

The message from alan@darkroom.+.com (A.Lee) contains these words:

Not that I know of. It may be that the socket has already been buggered up [1] by someone else.

[1] That's a technical phrase, by the way.

it sounds like you need a 7/64 allen key. This is right in between 2.5mm and 3mm (2.78mm)

available for 15p from here:

no doubt any good tool shop would have one.

mrcheerful

I've just checked it to make sure, and imperial allen keys are available in 64th sizing. I'm sure they're not common in the standard sets of allen keys (32nds is the common sizes available IIRC), but they are available. And having done a bit guessing, a 7/64th (2.78mm) is probably what you're looking for, which is a Nominal 6 according to

More likely the bolt heads worn. A comprehensive set of AF sizes is quite large though, it's 25 peices, most places sell you a set that misses out the rarer sizes.

almost everything sensible.

Try a 7/64". Near enough 0.1094" Mike.

Heat it up with a blowlamp and batter the nearest - tight, size into the recess. Unscrew it when it's cooled down,(wonder if it's left hand thread-might be if it rotates anti clockwise). If that fails drill it and use a stud extracter. (When the only tool you have is a hammer, any problem looks like a nail). DaveK.

Why are these called Allen keys. Was Allen the name of the inventor?

Nope, they where made in the US by Allen Manufacturing, in Europe they're called Unbrako keys