Slighty rounded allen key hole

[jakesi]

Is there any tool you can use to undo a slighty rounded allen key bolt (5mm and made of alloy)

[rekstout]

If the socket for the allen key is stripped then you may have no luck finding a key to fit it. If the head of the bolt stands prooud from the surface then you could take a hacksaw to the top of the bolt to cut a groove in it which can then allo the use of a flathead screwdriver.

[sft42]

you could try a torque driver bit and see if this fits....usually are available with good ratchet sets.

[xyzzy@bok]

impact driver or reverse drill it out. maybe.

[sddsddean]

As long as you can get a replacement bolt, try filling the hole with Araldite and gluing the allen key in. Leave it for at least a day(preferably 2) before you try unscrewing it. You should be able to rescue the allen key by sawing through it just above the bolt. Otherwise, its a case of trying the next allen key up, a torx socket or one of the other suggestions to try and jam something in the hole.

[cucumbers]

Depending on the quality and hardness of the steel that the allen key bolt is made from it may be possible to drill a hole down in to the shank of the bolt , say a 3mm hole , with a good quality metal drill bit and then use a screw extractor , which is basically a tapered, hardened steel drill with a left hand thread that you wind into the pre-drilled hole until it bites and then the turning force will unscrew the bolt. Any good tool supplier / hardware store should sell a set of these extractors and you should get a set with about 5 different sizes. If i recall , Record Marples manufacture them.

[asallen]

Take a parallel punch, same size or larger than the head of the bolt. Using the punch and a hammer give the bolt head a couple of sharp taps. (be brave!). this will spread the head of the bolt and at the same time will loosen the thread. Use a "socket " type allen key with a ratchet or small breaker bar. This way you can tap the allen socket into the now slightly deformed allen bolt. repeat the process if you round the bolt head. This will work!!!

[paulz]

If it's a flush socket, try wrapping a thin strip of emery cloth/rough wet & dry around a smaller allen key, this should allow you a good internal grip. Give it a good soaking with releasing oil first [3 in 1, WD40 etc] Get a new bolt too! Good luck