Splais..they are metal washers with neoprene on one side..They are slightly concave..I think thats what its called[&:]

Anyway when you tighten them down they compress..sort of like a split washer..You have to use blind nuts but believe me I will never go back to wood screws...Ive used the cowl binders before and they do work pretty good but not like these washers..I havent had one come loose in over 100 flights on my WH Edge..

http://www.microfasteners.com/catalo...ts/WASFWRB.cfm