Large 7-1/4″ x 13″ x 3-1/2″ seat mounting platform. Travels 5-1/4″ forward and backward with 8 locking positions. Rotates 360�. The pivot handle rotates with the chair. Mounting pattern: 4″ x 5-5/8″. Universal mounting pattern: 5″ x 5″ and 5″ x 12″. Easy to install and remove with a separating lower mounting plate. Bulk. ABYC Class: (AD) H-31 Driver.