Lisle tailpipe stretcher part number 34400. I purchased to elimiante the leakeage between my headers and side pipes on my BDR. Works like a dream, only used a cresent wrench with the tool. Can be used with impact. This tool list for $130, sell most places for $80. It is new. This is not the cheap autozone or harbour freight which breaks or the threads strip out. You can use in an impact but I feared it would expand the pipe to quick and tear the pipe. Do a search on google under the aformentioned part number and you will see this is used in place of hydraulic tail pipe expanders.
