Stair Climber Castor Units are made up of three ru... Read Morebber tyre, metal centre wheels in a triangular formation housed in a 3 point  'star' shaped steel frame with a central bore fitted with a quality 20mm needle roller bearing. They can replace existing wheels on a sack truck with a 20mm axle. The hub length (distance through the central bore) of the unit is 60mm.Stair climbers are used on sack trucks to help move heavy loads up and down stairs. The load capacity of this product is 140kg.