Well I was in luck. I have another Burnerd 4" chuck, well used that is permantly set on a homemade tool. I had the outisde jaws for that chuck and a few measurements showed they should fit, needed to file burrs of the new chuck body but after 5 mins work with a fine fine and a good clean and they fit great, looking like they centre very well also. I will grind them in situ when i have a chance just toe make sure everything lines up nicely but in all I am happy and it didn't cost me £150!