A family of Buick engines that have vertical valves, a pent roof combustion chamber . The distributors were in the rear and the starters were on the drivers side(unlike later Buick engines), they were made from 1953 to 1966 in 264-322-364-401-425 sizes . There were other size Buick engines that resembled nailheads like the 215 and 300 V8’s but have no parts interchangeability with the nailhead. They are in fact related to the V6 and later Buick V8 .
There are many different parts used on the nailhead, many changes from year to year so please state the year when asking questions and ordering parts. For example, there are 4 different 401 engines.