

Selden gooseneck joint or universal joint . This stainless steel part consists of two shafts. One vertical shaft, 6mm in diameter, for mounting on the mast. The other horizontal shaft, also 6mm in diameter, is for mounting on the boom: specifically, the Selden 509-081-09 gooseneck with its sheaves for the Gnav system.
The central axis of this joint (8mm in diameter) will allow you to pass the end of the main sheave through to ensure the continuity of your adjustments.