Except for maybe Nordloc's, lock washers are poor keepers in critical situations. Split locks are really bad, as mentioned before, they break out from under the fastener (or can, especially if reused). The "spring" in the system should be the bolt. If the bolt isn't long enough to be the spring, then another method (mechanical like safety wire, cotter pins, lock nuts (all metal top locks for larger than 5/16, nylocks for under), etc. or chemical like Loctite) is a better answer. You don't see lock washers on the rotating parts or head bolts of an engine. Pan bolts, while important to keep the juice in, or anything across a gasketed (I.e. movable) surface doesn't classify as a critical joint, so maybe split locks function (my experience is the torque spec is so you don't split the gasket, not to keep the bolt tight). There may be some marketing that promotes split locks as an enhancement, if for no other reason than the function is intuitively obvious. But blood letting had proponents at one time also. We could go into the reasons that torque is a craptastic method of measuring clamp load, which is really what we are trying to get to, in an effort to make enough friction to keep it all together but that's a whole 'nother discussion. And yes, I am an engineer - don't pretend to know everything, but I didn't learn everything out of a book either (most of the engineers I work with can't spell lathe, fewer actually use wrenches to work on anything, and I cuss engineers more than most people do because of it.) We build primarily off-highway trucks with no rear suspension, lock washers are not used - anymore.
