Reduced head screw

I’m about to drill and countersink for the flush AN509-8 screws behind the baffle on some RV-4 style fuel tanks. The plans call for AN509-8 screws but I’d like to see if there is an alternative with a shallower countersink. Will a NAS8602-1 or -2 work?

Getting into the weeds here. Thanks for the help!

Jay

Here is one of my old posts for reduced head screws I used

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Old 01-07-2014, 09:46 AM
fixnflyguy fixnflyguy is online now
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,265
Default Titanium hardware
I have used the Boeing fastener codes/sources for all my Titanium hardware. Again, being in the industry helps, and for the most part, an RV uses 2 basic types, one being the hex head bolt, and the flush machine screw. I simplified the flush screw variations throughout the entire plane, and utilize all #8 screws/nutplates for fuel tank attach flanges,fairings,wheel pants,floor panels,ect.. But I used what is known as a "reduced head" 100 degree fastener. These screws have a smaller head that is equivelent to a #6 screw, but have a 5/32" shank diameter. The hex head bolts are a direct replacement for the AN3&4 diameters. The basic numbers are:
Hex head bolt : BACB30NR (diameter in 16ths)K(length in 16ths), so a BACB30NR3K3is a 3/16 diameter, 3/16 grip length Titanium bolt with aluminum coating (the K designation).
Flush head: BACB30VF2K3 is a reduced head,100 degree CSK #8 machine screw, 3/16 grip. The (2) diameter is for a 5/32" diameter, however a (3) would be 3/16", so dont let it throw you off. I know this is all a little confusing, but Google the numbers and you will probably find vendors/data..but I would start with the originator of this thread.
__________________
Bill E.
RV-4/N76WE
8A7 / Advance NC

I used some NAS8702U1 reduced-head fasteners on one area of my RV-3B. These have #8 threads with a #6 head. The material is A286 stainless, at 160 ksi. This is the material and strength that most of the spacecraft I worked on in my career used for their fasteners - tough and strong.

My source was Military Fasteners. There was a minimum order. These weren't cheap.

Thanks to HFS for the fastener suggestion.

Dave