The Royal Enfield has used several different thread types over the years. In the late 90's most of the bike itself was some form of metric thread and the engine was mostly Whitworth.
Currently the entire bike, engine and transmission are "mostly" metric. "Mostly" is the key word here. We use this metric thread pitch every day in our shop to determine threads.
Royal Enfields do not always use the most common metric thread pitch sizes, so this tool has become invaluable. High quality, with 20 different metric thread pitches represented.
Every toolbox needs one of these!