Sheet Metal Screws

[Jim Fulton]

There is a discussion in another online forum about mounting hardware on aluminum spars. The consensus there seems to be that sheet metal screws are superior to machine screws because the threads are deeper. This concerns me. Is there any engineering data available on the holding power of sheet metal screws vs machine screws in aluminum about the thickness of the average spar--say, about 1/8 inch? I know that the sheet metal screws are often more difficult to remove and that they can tear up the aluminum. When I overhauled my mast, I replaced all of the sheet metal screws (many installed by the builder) with machine screws, but I don't know of any data on their relative holding power.

Jim Fulton