You may have Plillips Pan Head fin screws in your board (s).
These safety washers were originally developed back when Starboard
supplied hex head fin screws. The Hex head "points/corners" were sometimes
pretty sharp so they developed the safety washer for that reason.
Also some of the flat washers (they are punched out in a punch press and
then tumbled to dull the sharp edges) have fairly sharp edges.
Sometimes, if you do not use a high quality #3 Phillip Screwdriver, the Pillips
pan head screws can get some burrs on the top of the drive recess and those
can be sharp as well.
The normal "stack up" is:
1/ The fin screw
2/ The smaller washer that will fit inside the safety washer
3/ The safety washer
No need for anything under the safety washer if you have an EVA
deck in the fin screw area.
The reason you need to "seal" the fin screw holes is to prevent the
vacuum that develops on the upwind side of the fin from pulling air
down through the fin screws and along a poorly fitting Tuttle fin head.
If air is drawn down this negative pressure path, then your fin will "spin
out' rather dramatically.
Hope this helps,
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