Been tinkering in engine bay was putting strut brace back on, then as i was tightening up the nut for the vacuum box the screw sheared off. Can a new one be welded on if so by who?

Am i the only one to do this?

not got my car so cant look but can you not drill / tap it out? or is it needed to be in there? 

On the back of the frame onto the bulkhead?

It was the little black one on the firewall that the vacuum box bracket slotted over then little nut went on to hold it in place. Never felt like it was tightening this time though and it just came off the body.