What would right terminology be for one of these:

http://www.m1911.org/images/cpart2.jpg

of course, I'm referring to the side mounted sight rail (picatinny on top?)...there must be an official name for these types of mounts that show up on race guns...I ask because I'd like to find a vendor and buy one for my Colt that I'm building up. I imagine it requires smithing...I'm not concerned about that. I've done a ton of searches on various names of what I'd call it...but nothing that anybody actually sells has turned up. Just some nice pics of some seriously bling-bling guns

Thanks