Made from aluminium. Has a rubber pad on the bottom where the piston head connects together with 2 o-rings for improved compression. Easily the most popular cylinder head.
Due to the slightly thicker o-rings I find the SHS / Rocket version to be tight on cylinders which have an internal diameter or 23.8mm or less. All manufacturers tend to differ slightly so please check. A good alternative is the XT cylinder head which uses slightly thinner o-rings but is identical. Works very well with XT cylinders.