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Fuel tank screws

kmwoody

Member
Hi, I removed one of my tanks to replace the sender. The screws were triwing security screws and were very hard to remove. I decided not to reuse those screws and buy replacements.

I searched on Van's forums to see what # screw I should use. The recommended screw was AN509-8R8 or MS24694-S5.

When I received the screws they were different than what was in my tanks. The screws that came out of my tank were 10-32 reduced head screws.

I believe my tanks were built mid 1990s.

Does anyone know if this type screw was used in the past and have a part number or where I might purchase some?

When I tried a standard 10-32 screw in the tank, the head protruded slightly, while the reduced head screws were flush.

Thanks for any help/advice.

Ken W
 
I have some..its an exclusive club!

The reduced head 100 degree CSK screws are the mainstay of all heavy jets, and the Tri-wing was a Douglas and Lockheed favorite. My day job is maintaining the KC-10 tanker,so I see them daily. Boeing also has a normal Phillips head reduced head screw, mostly all are titanium, which is what I have on my -4 in every flush screw hole. I made everything a #8 on mine,so one screw fits all. My tanks use a #8 thread which has the same CSK profile as a # 6 standard CSK screw. Who ever built your plane was certainly a heavy jet guy. I also have a zillion Tri-wing bits if you need to re-use what came out to match the other wing. We commonly refer to these a %&*$%# screws for a reason. They are actually fine if you do everything correctly installing and removing them. ALWAYS dip your screw driver tip in valve lapping compound for bite.PM me if you need help!
 
Thanks for the replies.

I just knew they had to be very special use screws, thanks for the info.

I think my best, most economical option, will be to drill out all the -10 nut plates and install -8 nut plates and AN509-8R8 screws. I bet those Triwing screws are expensive.

Thanks again guys,

Regards,

Ken W
 
Thanks for the replies.

I just knew they had to be very special use screws, thanks for the info.

I think my best, most economical option, will be to drill out all the -10 nut plates and install -8 nut plates and AN509-8R8 screws. I bet those Triwing screws are expensive.

Thanks again guys,

Regards,

Ken W

That won't work since those holes are not sized for a #8. The hole carries the shear load, not the nutplate. You are stuck with the #10. as mentioned, Gen aircraft hardware is probably your best bet. Luckily, the tanks aren't off and on very often.
 
PM me..

Ken,
Send me a PM with contact info and I can probably help you get some replacements..as mentioned, you need to keep the shank/hole size matched to carry load.I can likely get you converted to phillips head and get away from the Tri-wings if you so desire.
 
More important info

Thanks again guys,

Thanks to people a lot smarter than me, I was concentrating on the flush countersunk head being the same size.

Glad I didn't start drilling rivets yesterday.

PM sent to you fixnflyguy

Ken W
 
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