A Lincoln Locker is named such after the Lincoln Welders and is called this because it is literally nothing more than welding together the parts inside a carrier to make it act like a spool. Therefore the axle shafts cannot move at different speeds, and you essentially have one solid axle shaft. This "poor mans locker" is less reliable because: a) welding weakens the gears and b) the stresses introduced by this spool effect often exceed the design specs of the differential's gears.