Dimension is the distance from bottom of this air cleaner base to carb neck sealing flange with spacer listed. OD is 14.25 in with a 1.25 in flange. 1/2 spacer places base 1-1/8 below carb neck 1 spacer places base 5/8 below carb neck. 1-1/2 spacer places base 1/8 below carb neck. 2 spacer places base 3/8 above carb neck.