scope:

Description of Driving Event:

Galling of threaded fasteners was experienced in the qualification test program of the Z1 Truss. Fasteners intended to be removable on-orbit galled during test. The fasteners were installed in locking threaded inserts ("KEEN" type).

Root cause: The inherent effect of the "Keen"-type, upset thread design is to bite hard into the fastener. After repeated installation and removal, the fastener will gall. These inserts work best engaged once, and are excellent in this application.