Four-hole aluminum spacer angles the carburetor left and to the rear so the carb is closer to level when in race attitude. Spacer accepts 1/2" or 1" tapered inserts which can be changed quickly by removing the carb. Inserts restrict air/fuel entry and reduce power slightly to prevent wheel spin and range in size from 0.950" to 1.400" for custom tailoring and quicker lap times. Spacer works with most Holley 4bbl. 4150/4160 series carburetors. Inserts sold separately.