Abstract: A roller reamer for an earth boring tool is provided in which rollers are carried by shafts in pockets in the reamer body. The shafts are supported in bearing blocks which have segmental cylindrical surfaces at their widths, and a relatively shorter length as measured along the axis of the opening in the block for the shaft. The bearing blocks are passed through an entryway communicating the pocket with a recess adjacent the end of the pocket. The bearing block is passed through the entryway in a position transverse to its operative position and into the recess, and is then rotated in the recess, by cooperation of the cylindrical walls of the bearing block and mating cylindrical walls of the recess, to the operative position. The movement of the bearing block is readily achieved since it has a clearance fit with the recess to permit free assembly and disassembly of the bearing block.