APD's Billet under carburetor throttle stop is made from 6061-T6 in house on our 4-Axis machining centers. 2.155 bore is standard and custom bores are available. A merge spacer is built in to obtain maximum HP. Supported 1/2 throttle shafts and roller bearings makes this the most precise rigid throttle stop on the market. They are available in both 2-3/4 and 1-3/4 heights, and C02 or electric.