21mm aluminum nozzle with a single o-ring designed to be more resistent to oil / temperature and generally provides a longer service life, helping to keep a better air seal and nozzle alignment.
Our nozzles come with 2 o-rings, essentially a fat and a thin one, this gives you a choice of fitment since the outer diameter of cylinder head shafts can vary. As always please ensure you use small amount of silicone grease on the oring