AI says:  This cap typically fits passenger cars and light duty trucks from the muscle car era and classic era (roughly 1968-1978) with unthreaded, twist on filler necks the require a shallow cam locking engagement.

Will fit a lot of GM, Chevelle, Malibu, El Camino, trucks and SUVs.

Will also fit Mopar and Chrysler products.

The cap measures 3 1/2" in diameter.