The 10 inch ID, 110 tooth ring gear is the most common size for the Formula Ford 1600 engine. This ring gear has a special double-tooth chamfer to work with both Tilton (pre-engaged) and Lucas (inertia) starters. The ring gear should be installed so that the starter teeth make contact with the chamfer (on the intake side of the FF1600 engine, the flat side of the teeth should face up, with the chamfered side facing down towards the starter).
We also offer a stronger FF1600 High-Strength 110 Tooth 10 Inch Ring Gear (Part No. 163-07), which lasts longer when used with the Lucas inertia-type starter. This type of starter spins before engaging the ring gear, which wears the ring gear teeth.
Note: Some later cars use a 10.12" ID 110 Tooth Ring Gear (Part No. 173-03), and some later British formula cars use a 132 tooth ring gear. Be sure to check your car before you order.