Rigid makes an attachment gear for threading 2-1/2 thru 4" galvanized rigid. Trade slang is I think hog leg. I just now walked into my shop to look at the model number. 4P-J . You use it in conjunction with a Rigid 300 and a porta pony threader. A new one would be way too pricey if you only are using it this one time. Some hardware stores have a stand up threader that threads up to 4" for threading pipe they sell. Call around.
