I'm hoping the chuck body will be soft enough to turn out the existing thread (with carbide) and insert a plug with the correct size thread.
I bought one a couple of years ago, of Indian origin, for 40-50 quid
The back/black part is case hardened and is rock hard (I tried to drill mine with hss so it had more tensioning bar holes- not a hope), they are chunky and strong for small chucks.
Assuming they are still the same you will need carbide tooling and a good lathe to muck about with the black part
The main body appears to be made of a good grade machineable steel so a new plug should be possible
Edit: Just realised, Mine is the 50mm version
Edited By Ady1 on 09/08/2015 01:39:59