I have read the article about plug welding and found it informative. Now the only problem I seem to have is the hole size, the flange I want to weld is 10mm wide. So I feel that a hole 7.5mm in diameter would be too great. Would 7.5mm be ok or what dameter hole would you recommend? I am welding an inner sill to a step sill on a mini so the steel is not that thick.