Grass trimmer connector (7 teeth to 9 teeth)

Prehistory:

I bought two trimmer heads (chainsaw and brush cutter) for sale at a very good price.

But the shafts did not fit together with my trimmer. So I made this connector.

How well does it work:

It works surprisingly well, considering that I use it a lot. Connector broke only once when the saw jammed in the cut. In fact, he played role of a fuse.