Roller wheels attached to the gate support post. These support the gate at the top and support it vertically. No load is applied to these besides side loading holding the gate vertical. Made of nylon, they are durable and minimise damaging the surface they are rolling on, particularly powder-coated surfaces.
Picture for illustration purposes, colour may vary
The guide roller is available in two sizes, 40mm x 30mm or 60mm x 40mm