The "Governor" is a 1" thick, four-hole aluminum spacer with replaceable tapered inserts (sold separately) which can be quickly changed after carb is removed. Restricts air/fuel entry and reduces power slightly to prevent wheel spin. Inserts range in size from 0.950" to 1.400" for custom tailoring and quicker lap times. Fits all Holley 4bbl. 4150/4160 series carburetors.