Screw Sizes/Sources

[170C]

I have purchased the outer ring screws for the fuel tank adapter (AN 520-10R10) 8 each side. Got them in stainless so as to help prevent rusting. (Any good reason not to use SS screws in this application?) I have not been able to find SS screws for the (6) ones needed for the AN 520-10R10C. For clarification, are all 14 of the screws that are used with the fuel tank adapter the same size? If not, what is the difference in the 6 that are down inside the adapter vs the 8 that are on top? If they are of different sizes, suggestions for sources in SS? Van Brotal & Tex-Air don't have them or access to them. Finally, any reason not to use SS screws to secure the fuel tank covers?

[GAHorn]

The AN520 series is a fine-thread, pan-head screw. The "modern" replacement is a MS35207. So a AN520-10R10 should cross-reference to a MS35207-264. A stainless version would be MS35207C-264.

You would probably also be satisfied with a MS27039C-1-10. The difference is that this screw is mfr'd t o 125,000 psi tensile strength instead of the 55,000 psi of the specified part, and it is available from Spruce for 11-cents each. 877-477-7823

[cessna170bdriver]

Frank,

Try General Aviation Hardware Co. in Paso Robles, CA. They have just about anything you might need in the way of AN & MS hardware. For reasons he posts on his website, the proprietor of GAHCo closes both his physical store and web store on Saturdays, but he's up and running the other 6 days.

Miles

[n2582d]

I have purchased the outer ring screws for the fuel tank adapter (AN 520-10R10) 8 each side. Got them in stainless so as to help prevent rusting. (Any good reason not to use SS screws in this application?)

Frank,
Are you planning on adding nutplates to the adapter ring? If so, the machine screws you ordered will work. But the parts book calls for PK76XZ-8-10 sheet metal screws rather than machine screw for the 8 screws that attach the adapter plate to the top skin. These are #8 PK screws which are 5/8" long. A current p/n in stainless would be 04-00007 from Aircraft Spruce or HD 8RX5/8TBS from Chief Aircraft. Don't get the pointy "type A" sheet metal screws and double check to make sure 5/8" is not too long--you don't want 8 little fuel tank "vent holes" beneath those screws! If you want to get real fancy you could put nylon washers under the screws to limit dissimilar metal corrosion between the stainless screws and the aluminum fuel tank cover. They are p/n 04-00217 at Aircraft Spruce.

Truss Head sheet metal screw.jpg

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