The first crucial aspect to keep in mind is the proper installation of the mast in the board - make sure its fully inserted in the tuttle box, and at the desired angle. It's essential to ensure that the cross dowels are correctly positioned and facing the screw mount openings of the tuttle box to the deck of your board. Check the angle of the screw entry and make sure its not excessive, as that could cause crews to bend or break. With the mast fully inserted and properly seated in the tuttle box, use a caliper to measure from the top of the board (the deck), all the way through the cross dowel to the bottom of each screw opening in the mast. Then, subtract 3 to 5 millimeters from this measurement to determine the appropriate length of your mounting screws.
For the attachment to be as strong as intended, it's imperative that the screws pass completely through the cross dowel. With the right screws and a secure fit in the tuttle box, you should be in good shape. Regularly inspect all the fasteners on your foil to ensure they are in good condition, and remember to lubricate them regularly with products like tef gel or marine grease.
I personally have reservations about using rubber washers, as they may not necessarily offer any substantial benefits. Their only potential advantage might be to safeguard the board's paint around the screw hole, but even this isn't a certainty. In contrast, I prefer using stainless steel washers.
Note that fasteners and any damage or loss resulting from their use is not covered by F4 warranty policy. Please always contact our technical support if you have any questions or doubts.