An H-16 is a 1656.
Just to let you know there was no H15 there was just the 1556The H14 (1456) or H15 (1556) parts manuals will serve. Only the engines differ.
How it locks:
On the right side the hub is always keyed solidly to the axle. On the left side a tapered brass cone is always keyed solidly to the axle.
The large wingnut forces the tapered brass cone into a matching tapered funnel machined into the left hub. The friction locks the left hub to the axle. Then you can spin both wheels when you lose traction.
Oh. Right. Sorry.Just to let you know there was no H15 there was just the 1556