It is a Castor in showcase system. It acts as a wheel. The castor is assembled into the screw hole of bottom corner for showcase or the bottom of the extrusions. After assembling castor, the showcase can be pushed freely. Select castors different castors who has different diameter screws according to different screw hole diameters of bottom corner for showcase. It weighs 0.046kg per each. Its screw’s diameter is 8mm. It is plastic. The products of LingTong are green and environmentally friendly. If there are some relative needs, LingTong will provide the best service for you in exhibition construction.