Axle bearing block with symmetrical design. This allows for ajustable wheel height without the manufacturing of a completely new frame rail by rotating/replacing the bearing block. Weight is reduced by machining a slot completely through the block without reducing strength. Design shown is for a “dead” (i.e. non-rotating) axle, but block is wide enough to pocket both sides and add ball bearings for two-point support of a “live” axle.
Referring to discussion of overall design here.