This is the long splined shaft with a sixteen inch gear at one end.
Mariner, Dave unicycle manufacturer since 1969, made the first production unicycle with a splined axle.
This is the long splined shaft with a sixteen tooth spur gear at one end on which are mounted the other countershaft gears.
There is a punch mark on the chrome lever which aligns to a similar mark on the splined shaft.
While the splined hubs for the wire wheels were restored by zinc plating.