These are the R6 length stainless steel machine screws used to fasten the majority of the sheet metal panels to the fuselage. The nylon washers protect the paint from wearing away underneath the truss head of the screw.
The longer R8 screw works in places where several pieces come together or where the shorter screw won't reach.
Sheet metal screws
Most of the trim pieces attach with sheet metal screws. The rear part of the metal fuselage, where the covering transitions into fabric, is attached with #4 sheet metal screws, not machine screws.
I use the smallest screw that will tighten, then go to a longer screw up to 3/8", then go to a larger screw. These screws tend to loosen up and fall out with repeated removal and installation. I also use Permatex thread locker blue for screws that won't stay in, before making a step up in size.
Sheet metal screws have points. Aircraft Spruce calls these "Type A." Do not confuse them with tinnerman screws, that have square ends.
The screws holding the banana together were originally machine screws threaded through the fiberglass. These were forever falling out.
My solution was to attach some Tinnerman nuts on the back-sides using black Permatex Gasket sealant. The 3/8" Tinnerman screw worked best for me here.
Aircraft Spruce catalog pages: "Type B" machine screws and Tinnerman hardware
