The Black Inc Seatpost Outer Rail Clamp Set is designed for Black Inc seat posts which use the 1-bolt design. The clamps are offered in both 7x9 (oval) and 7x7 (round) versions. The 7x9 outer clamps are designed for oversized carbon rails while the 7x7 version is for traditional round alloy rails.This item comes as a set and does not include any screws, washers, and nuts.