These seat spacers are designed for a standard 10-inch canoe seat. The D2C spacer is 2-1/2" at one end, 2-3/4" at the other end. The D3C spacer is 3-1/2" at one end, 3-3/4" at the other end. Both have 8-1/2" on-center hole spacing. Sold in separately without hardware.