The right hand side self extracting crank bolt has rounded off on my X type cranks and I cant remove the crank arm. Any ideas how can remove it?

Would a stud extractor work?
http://www.wikihow.com/Use-a-Screw-Extractor

Hammer a suitable sized torx bit into it and that should shock the stretched bolt and the torx splines may grip the edges enough to loosen it, that’s if you already have a suitable sized torx bit and preferably of 3/8th drive.

A T50 torx bit may grip the rounded head otherwise an m10 spline may fit, i have x-type cranks and a T50 fits the head of the bolt, the m10 spline would prob fit if i had a rounded head and resorted to hammering it in

And don’t use normal allen keys, get a set of hex socket bits.

Screw extractors will not work as the depth of the bolt head is not enough, and a set of decent quality bolt extractors cost more than a set of X-type cranks.

would removing the cap help?

Ive used a stud extractor on one they are made of the most useless soft alloy.

Thanks for the info.

I’ve tried removing the cap with a peg spanner but it wont budge.

Will look into the stud extractor and torx method.

If you can remove the self extractor cap, the torx is the most obvious answer, failing that, drill time!