【No deviation from the track】: Installing our olive rail can help your gate stay on track when opening and closing manually or sliding the gate electrically, thanks to the "extended" nylon rollers mounted on the axle, which rolls by itself and allows your gate to slide.【Complete Accessories】: Pack of 4 sliding door guide nylon wheels (4 units). 40mm x 40mm.【Material】: This nylon swivel caster is made of nylon material with high strength and high density structure, stable performance and long service life.【Good Performance】: Our nylon olive guide is made of sturdy steel with strong bearing capacity, good elasticity, high toughness, no deformation, wear-resistant, corrosion-resistant and so on. The outer surface of the bearing is smooth, which can reduce the noise generated by the sliding friction of the iron door. It can be used indoors and outdoors.【Structure includes】: Nylon inner body and tread for smooth rotation. Nylon is a strong material that is resistant to impact, abrasion, high and low temperatures. It is also resistant to chemicals. It is the best substitute for wheels when they are worn or damaged. Suitable for electric doors, sliding doors, etc.