My experience comes from years ago disassembling some various plumbing
parts. Cast fittings could be removed by holding a sledge hammer to one side
and hitting the other side with another sledge. It didn't take much to crack
the fitting open and off the pipe. Malleable fittings were another story, no
matter how many times nor how hard you hit them they would not crack. If you
hit them too hard they would actually bend or deform. The only way was to
unscrew them, and do it before you bent it. Malleable usually means they
were shaped by forging increasing their strength, while cast items were just
poured into a mould with no strength.

"Smarty" wrote in message
...
I'm installing some black gas pipe(1" size) and find two types of
couplings being sold, one of which is called "malleable". I know what the
word means, but wonder under what circumstances this type of coupling is
preferred or should be used.

Thanks in advance for a reply.