IMPORTANT - The captive part that is to be bonded into the fin is correctly sized to fit the original SAILSetc fins and has a length of 5.3 mm to match the local thickness of the fin. This allows the captive part to fully penetrate both skins of the fin so that its ability to resist the load of the ballast and retaining screw is maximised. Where the fin is thicker (other manufacturer's fins and M-370-2019) the captive part may not penetrate, or fully penetrate, the skins of the fin and the retaining power will be much reduced. In this case the caprive part should have a 6 mm ID tube added to it that is long enough to extend fully through the fin. A short piece of SAILSetc 8 mm carbon tube, or metal tube, is suitable for this purpose.
This is the length of stainless steel studding, stainless steel insert and retaining nut that we use at the bottom of our fins when the ballast is to be removable. The stainless steel insert is bonded into a round keyhole in the fin and prevents the studding from pulling out. The retaining nut fits into a counterbored hole in the underside of the ballast. It is better that the counterbored hole has the brass seat, ref. INS-seat, fitted to resist wear.
The stainless steel insert is bonded into a round keyhole in the fin and prevents the bolt from pulling out. Make the hole in a strong part of the fin, through both skins and about 15 to 20 mm from the end to leave a lot of strength around it. To bond it in place take the following precautions: abrade the inside of the fin where the insert is to be bonded and clean with solvent, use thickened epoxy resin, push the thickened resin into the hole, add the insert, add the studding and adjust to length, fill any cavities with thickened resin and apply tape over the top, allow to cure well before attempting to add the ballast.