Application Inserts into bedframes which accept the square insert plug. Casters and glides which require the square insert plug are then inserted into the square insert plug socket. How Sold This item is packaged and sold as a set of 4 plugs. Thus, ordering a quantity of 1 will result in 1 set of 4 plugs being ordered. Ordering a quantity of 2 will result in 2 sets of 4 plugs in each set, or 8 plugs, being ordered.