Yes there are differences.See these two links for comparison.NPT
http:/en.wikipedia.org/wiki/National_pipe_thread
BSPT (PT)http:/en.wikipedia.org/wiki/British_standard_pipe_thread
With a stock and dies and a pipe vice or a threading machine such as a ridgid 300 or 400 or a 12 R or a 65 R depending on the pipe diameter and do not forget the oiler One can always use an Armstrong...
well 1st of all U need to determine the second pc. as a FITTING, and, after that if the two materials r 2 b used together it doesn't really matter. The best way is to stay with the original materials...