I want to loosen these end plugs on my 72 shovelhead to replace the O-rings behind. Does anyone know what size allen these are? They appear to be 9/32 which is basically an impossible size to find.

 

2 things - one its 5/16 the OEM allen socket and if you have some kind of Communist part on the bike that would be the real reason behind the leak

2 -- we use the nylon square seals not the o rings any more as they will always come back to leak again

 

You might find a hex bolt in your 20 year bin, use it upside down with vice grips, or double nut and wrench, or even pipe wrench to break loose.

 

^^ Extreme COB method...any hardware or autoparts store has individual allen wrenches...