Cross Manufacturing is a precision mechanical company based in Bath. Currently it provides valves and rings for the aerospace industry, but has a long history stretching over 70 years. It developed a rotary valve in the 1930's that heavily taxed the rings on the pistons, leading them to develop their own rings, which were used for years on Royal Enfields. A Crusader was used as a test machine and is currently kept in its museum together with an HRD Vincent. More here and here.
Road tested: Gear from Aether, Saint and Shoei
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