All replaceable bearings I know about are multi-layer, a steel backing, then a layer of copper or some other alloy, then Babbit, and finally a microscopic top layer of pure tin to allow the bearing to "wear in" to the exact shape of the crankshaft during the first minutes of operation. All the other terms are just advertising copy, thought up by someone who has never had his hands on a wrench!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!