Chevrolet 12-bolt Rear end 1965-72. 8.875-inch ring gear. Bolt hole diameter .437 inches. Spacer thickness .305 inch to .315 inch. Mr. Gasket stamped ring gear spacer is precision Blanchard ground to ensure parallel surfaces for perfect alignment. Kits are complete with spacer and bolts. *This spacer should only be used when using the Series Four Gearset on a Series Three Carrier. See image 2 for more information on the differences between the Series. The thickness of this spacer, .305"-.315", coincides with the difference between the series 3 and 4 Carriers. The Series 2 Carrier, being only a little over 1/2 inch thick at the ring gear flange, is not suitable for mid to high HP with slicks.