These Shims / Spacers are used on one side of the Engine only. This is due to the fact that the Engine mounts for the Datsun Roadster aren't identical on both sides, and installing one Shim / Spacer on the left hand side of the engine between engine mount and chassis is common. It is used to align the engine properly with the chassis. This is a two for the price of one deal! The Shim's / Spacer's are Powder Coated, and the holes are drilled.