[Plums]

Detroit lockers are street legal, as they still retain differential function.
I think you are referring to a spool (either full or mini-spool). Spools lock both axles together and are a real pain on the street, besides being illegal. Spools are great on the strip - had one in the Torana - but general street driving will cause an axle to break eventually. Many circuit cars use spools (eg. V8 supercars) because they are predictable and tough....