Folks should remember that Hurth
was bought by ZF and the model numbers have changed. Most Hurth
/ZF gears for apps under 50 hp are the mechanical type that carry the "M" for mechanical They have "Dog" type clutches that lock in position . ZF10M ZF12M etc.
These relate to the old Hurth numbers ZF10 = Hurth HBW100 The HSW designated gears were hydraulic
Also those that use engine water
to feed the stuffing box should lock the prop as there is no water
to lube the stuffing box with the engine
(" Honey, Whats that smell?)