Thumpalong

Hello I have a 08 hisun 700 and apparently that year they had frost plugs in the cylinder head and were know to corrode and start leaking. Well I have one and I have tried the jb weld to seal the leak but no go. Is there anyone that can tell me the mesurements of the cylinder frost plug hole. Apparently you cannot buy them not available, so I'll try to source something if I can get the mesurements. Thanks Thumpalong