Hello All, thanks for the replies. I found out that Dragonfly had inserts on their site and quoted the thickness as 7/32" (0.218"). I didn't know if the included a sanding allowance, I assumed not. I actually bought some 6mm cork sheet (450x300mm for £5.35 on e Bay enough to make 450) and made my own. I made a template slightly larger than the hole in the plate, it took about 3 hours to do the lot. 6mm is too thick as it will not allow the plates to fit in the confines of the chain wheel and basket. I think 5mm will be too thin not allowing for any sanding.
I have now re-corked all my friction plates and sanded them to 7/32", this gives 1/16" protruding each side of the plate, and they fit just about right. I did not realise at the time but the inserts in the chain wheel are thicker I'm going to make them 3/8" allowing 1/16" as I did with the others and see what happens. Either way I won't be far away.
I'll post the result I have tried it out, I'm assuming that as it is new cork it will settle in time under compression.
Regards
Pete