Is anyone able to tell me what size Allen keys are used on the kuryakyn hyperchargers? My imperial and metric ones don't seem to fit, are they maybe AF?

Mate, AF just means "across the flats". I have Kury also and cant remember what the size is. I will try and check it our for you when I have a minute.

bet it was a machine screw hmmm and probably a half size i.e. 6.5 still got a few allen keys from being an apprentice and have never used them since in over 30 years they have weinig stamped on them so gather they were for that machine manufacturer just typical of the germans but well made

Well ive been digging in the bottom of my old tool box thats about 30 years old and found 3 different size allen keys that has nothing stamped on it that seems to fit the 3 of the the different heads on the charger. But im still after a 4th one for the little bearing plate for the butterflies. I think a 7/64" ( roughly 3.75mm ) might do it which isnt a common size you buy in sets. I need to do a little on line shopping or go down to all tools and see if they have one I could try. 

Well just spoke to Kurykayan on line and they assured me the size Allen key I need is 7/64" So I gather the rest are actually an imperial size.  My Allen keys must be worn as they are pretty old. That's my excuse anyway. Lol