There are 2 plates. One attached to the rotor pipe and one to the boom.

Both connected together with bold and washer (M10)

A PDF drawing with the layout. (click)

Front side

The plate attached to the rotorpipe. On this plate there is a small rigde where the boom plate can stands on.

When both are in place you just have to places the bold and washer.

Back side or the side where the rotor pipe is attached to.

Boom plate with boom support pipe mounted.