the Brits say it tongue and groove, but our favourite Yank has it as tongue in groove. Who's right?

My stepfather is a carpenter (and he DOES call himself that), and a USn, and he has always said tongue AND groove (or, t-and-g, more familiarly), and he considers IN incorrect.

He also says rabbet and clamp, and has not encountered the Britforms of those two things, but I want to say that "rebate" is also a term in Classical architecture, but I don't have my dictionary here.

Also, to continue TEd's aside, my fractional math is also horrible, so I like decimals, too. However, my stepfather adds, subtracts, divides and multiplies complex fractions in his head as easily as I can manipulate integers. It's quite the parlor trick.