Abstract: A roller cutter assembly for use in hard rock tunneling machines comprises a rectangular saddle having a rectangular recess with V-shaped mounting surfaces. Support plates are secured against these mounting surfaces, and the support plates have a shaft extending between them with a non-rotatable head in one plate, and the circular nut in the other plate. The shaft mounts a pair of inner races for tapered roller bearings which run directly on the roller cutter inner surface which forms the outer race for the bearing assembly. Rotation of the circular nut in the recess and on the shaft sets the preload for these bearings. Between the nut and its recess on the adjacent support plate is an annular groove formed in both the support plate and the nut, and an elastomeric diaphragm fits across this groove.