A bearing casing assembly for a conveyor roller tube having a casing, a stub axle, bearings, an outer seal member and shield cap, is provided. The casing includes a body having a shoulder at its distal end extending circumferentially and radially outwardly for abutting against an end of the roller tube, an inner flange extending circumferentially and radially inwardly near the distal end from the casing body and an internally threaded a proximal end. The casing also includes a casing seat having a threaded portion for threadingly engaging the threaded proximal end portion of the casing body and a bearing engaging portion adapted to abut the bearing for selectively adjusting a preload on the bearing by rotating the casing seat about the casing body. The bearing casing assembly may further include an inner seal member when fluid lubricating bearings are used.