Those are pretty easy to service. All you need is a plumbing wrench (adjustable wrench) or vice grips, and maybe a flathead. Some modern bmxes and children's bikes still come with those. The big ones are called "ashtabula" or American, and there are also smaller ones that are pretty much the same, just smaller.

http://www.parktool.com/repair/printhowto.asp?id=92