You can use one of a number of types of mosfet in place of the standard ones on the RAMPS board.
The standard ones are
STP55NF06L. If you're going to buy these, make sure it's got the L on the end, otherwise it won't work.
That said, I'd recommend either using the
IRLB8743 or
FDP8870. They're both fairly close in performance to each other, and they definitely out-perform the
STP55NF06L's. The price for each wavers a bit, so at times I've seen one cheaper than the other, then flip-flop a few months later, then back again.
They both have lower on resistance (meaning they don't warm up as much, and they drop less voltage so more gets to your outputs), and both will happily work on a RAMPS board. Insert them in the same orientation as the original mosfets.
FWIW: Gen7 uses the IRLB8743 with good results. [
reprap.org]
Edited 1 time(s). Last edit at 11/03/2014 08:59PM by Cefiar.