You can call the people at Tillotson to get the right parts, actually talk with a human. Have the carb model/serial # handy.Watch out. Zama used two different shapes of welch plugs in the C3 carb (assuming that is the one that you have). As far as making a welch plug fuggetaboutit! BOTH Walbro and Zama can't get the plugs to seal reliably using precision parts and factory tooling. They use a proprietary secondary sealant. Once you get the correct plug installed run a THIN bead water THIN of super glue around the edge of the plug. Put the carb on a shelf for 48 hours to make sure that the super glue cures completely. Be sure to clean the new plug and the recess in the carb with brake cleaner before installing.
Didn't know Stihl bought Zama. They got a Chi-Com factory?