The castors have a single M16 hole on the top plate, they are supplied with a 10mm thread for fixing, the mounting plate is pressed steel & the body is cast aluminium. There is a 1 year warranty against any manufacturer"s defects. The castors are easily adjusted using the hand-wheel incorporated into the body, when the rubber pad is screwed down the unit is fully immobilized & the rubber pad also acts as a vibration dampening mount. These castors are used for applications where the unit needs to be mobile & also needs to be fixed in position on feet.