Seat binder bolt question

[flash]

I've got a David LLoyd track frame I'm building up. I've exhausted my collection of binder bolts and none fit. Does anyone know anyone who sells a selection and haw I can find out which one I need. It's 20mm caross and has no threads, so I guess it's an allen key type.

 

[hamster]

You'll normally find that one side has a small slot in it - this holds a threaded part, the other side will take an allen key. Ask your LBS...it's the sort of thing they keep in a drawer!