The cover part is composed of a cover, a rolling bearing, a tapered sleeve, an upper bearing cover, an upper sealing ring, a round nut and a straight-through oil cup. The bearing cover is used for the outer circle positioning of the bearing. The inner linoleum groove in the bearing cover is used to install the linoleum to play the role of sealing oil. There is a raised ring outside the bearing cover to block the dust outside from entering the bearing cover. The bearings are lubricated with straight-through oil cup oil, and can realize the adjustment of the bearing clearance by adjusting the gasket.