The knockout pin for easier removal. 3/8″ Drive: 13mm, 9/16″(14mm), 5/8″(16mm), 17mm, 11/16″, 3/4″(19mm), 1/4″, 5/16″(8mm), 3/8″, 10mm, 7/16″(11mm), 12mm, 1/2″. 1/4″ Drive: 8mm, 8.2mm, 8.5mm, 8.7mm, 9mm, 9.2mm, 9.5mm, 10mm, 6mm, 6.2mm, 6.5mm, 6.7mm, 7mm, 7.2mm, 7.5mm, 7.7mm.