nylon wheel medium duty rigid castor 1)size:50,60,75,100mm 2)loading capacity:40,50,50,60kg nylon wheel medium duty rigid castor 1)housing:made of pressed steel, zinc plated, double ball bearing swivel head, medium duty version. 2)wheel: of high quality polyamide, with plain bearing, high abrasion resistance, low rolling resistance, impact proof and corrosive resistance.