Inch - Everything2.com
Inch Tue Apr 13 2004 at 21:35:59 Curiously, the inch is exactly 2.54 cm. The story goes that Henry Ford was frustrated at the lack of standardization of parts measurements and things; the US at that time used various different inches, while the cm was fixed. So Ford asked Swedish inventor Carl Edward Johansson to make some end-gauge for Ford's factories. Johansson was happy to, so while Congress mucked around trying to come up with a standard, he picked the handy 2.54 cm to an inch that we know today and delivered the blocks. The 2.54 conversion allowed a switch from metric to imperial thread...
Source: everything2.com