Fin Insert Bottom. A 50mm length of 3mm dia stainless steel threaded rod fits into a 6mm dia stainless steel insert which is bonded into the bottom of the keelfin.
The hex shaped long retaining nut fits into a recessed hole put in the underside of the keel bulb. To reduce wear in this area fit brass seat, Part # INS-SEAT.
For IOM/M/10R
Weight: 10g.