The chassis of the worm gearbox is usually cast from cast iron, with only a few heavy duty gearboxes cast steel. The deceleration casing is composed of two parts, a box seat and a box cover, and the split surface passes through the axis of the transmission. The holes in which the bearings are mounted on the casing must be precise to ensure positive solution of the mutual position of the gear axes. The box base and the cover are bolted, and two positioning pins are used to precisely fix the mutual position of the cover and the case. The arrangement of the bolts should be reasonable and the space required for the use of the wrench should be considered. The bolts around the bearing can be slightly larger in diameter and as close as possible to the bearing.