Porsche Synchro Gear Teeth, 2nd – 5th Gear 911 ’65-’71, 912 ’65-’69, 914-4 ’70-’76, 914-6 ’70-’72, Synchro Gear Teeth, 3rd – 5th Gear 911 ’72 – ’86, 912E ’76 – Symmetrical Tooth Point, One Slot in Hub. These synchro hubs or “dog rings” feature our exclusive differential heat-treatment process which produces very hard and wear resistant engagement teeth with somewhat softer internal splines to help protect and extend the life of your expensive free gear nose. Manufactured by us right here in Colorado from only the finest domestically produced alloy steel. Porsche never sold these as separate parts.