Wise 8WD562 Ladderback Helm Chair Shell and Pre-Mounted Universal Mounting Plate. Aluminum L-brackets connect back and arm rests to seat; Mounts to any 4 Bolt BIA Standard Pedestal System Thick wall rototional molded, high impact marine grade plastic external frame, includes a pre-mounted universal pedestal mounting plate with T-Nut insert Seat Shell Only - No Cushions Replacement Snap on and off Cushion Set available SEAT DIMENSIONS - Height: 21" Width: 17" Depth: 22" Sitting Depth: 15.5" Sitting Width: 15.5"