Cowling & Wing Screws?

[reecewallace]

I need to replace screws on my cowling/wings, but would like confirmation on p/n's before I order since the p/n's listed in the IPC are not popping up on ACS.

1. Cowling screws for 172 cowling & plastic washers
Stainless steel sheet metal screws #8 & #10
1/2" long
No idea the p/n??

2. Wing screws covering fuel tanks
Need stainless steel screw for this. See pics.

https://www.pinkbike.com/photo/26145933/
https://www.pinkbike.com/photo/26145931/
https://www.pinkbike.com/photo/26145929/

I believe the p/n's are:
NAS228-12?
NAS228-8?

Thanks

[cessnut]

The screws that hold the fuel tank cover on are NAS structural screws and should not be replaced with stainless steel hardware. These screws and the panel they hold in place perform the function of tying the front and rear spar together as well as the butt rib to the next outboard rib.

[reecewallace]

The screws that hold the fuel tank cover on are NAS structural screws and should not be replaced with stainless steel hardware. These screws and the panel they hold in place perform the function of tying the front and rear spar together as well as the butt rib to the next outboard rib.

Thanks for the heads up.

Do you know the p/n's? The two numbers the IPC gives are not found online.

[GAHorn]

MS27039C screws are stainless steel Manufactured to MILS6050 or MIL8695. Equivalent to NAS 220

https://www.aircraftspruce.com/catalog/ ... S27039.php

The cowl screws are common PK screws and plenty of SS are included in the kit (PN 04-01200) sold for the Cessna 120/140/170 series: https://www.aircraftspruce.com/pages/ha ... herkit.php

[c170b53]

I wouldn’t use stainless. Reese will likely find out how hard these screws are to remove if they have been in there for some time. Should the heads deform on removal, drilling them out would be easier if they are just plain steel. Of course opening panels / trailing edge and spraying your favourite removal juice will aid in the process.

[reecewallace]

MS27039C screws are stainless steel Manufactured to MILS6050 or MIL8695. Equivalent to NAS 220

https://www.aircraftspruce.com/catalog/ ... S27039.php

I'm confused—

The IPC lists the top wing screws as NAS228-12 & NAS228-8. I don't know if I need stainless or not?

What are the p/n's as the IPC lists two different screws for the top fuel tank wink cover?

[n2582d]

Reece,
The NAS228-8 and NAS228-12 are obsolete brazier head structural screws. The -8 indicates the screw is .531" overall length under the head, and the -12 indicates a length of .781" according to Genuine Aircraft Hardware. NAS228-12 screws are still available from Univair. Later Cessna 172's use NAS220-8 and NAS220-12 screws in this application. As has been mentioned, the superseding part numbers are MS27039-0808 and MS27039-0812. Aircraft Spruce sells Trimcraft Aviation's stainless steel fuel tank screw kit for the C-172 as p/n 04-01003. These are MS27039 screws which are structural. As Jim has said, I would be concerned about galvanic corrosion if using these stainless MS27039C0808 and MS27039C0812 screws. You'll find it much cheaper to buy the screws à la carte rather than as a kit.

[cessnut]

The -8 and the -12 are the lengths. You will need some of both. The MS part numbers that George mentioned earlier are what you need. As said earlier, I wouldn't recommend stainless if for no other reason than the risk of them galling in the nutplates.

[reecewallace]

Reece,
The NAS228-8 and NAS228-12 are obsolete brazier head structural screws. The -8 indicates the screw is .531" overall length under the head, and the -12 indicates a length of .781" according to Genuine Aircraft Hardware. NAS228-12 screws are still available from Univair. Later Cessna 172's use NAS220-8 and NAS220-12 screws in this application. As has been mentioned, the superseding part numbers are MS27039-0808 and MS27039-0812. Aircraft Spruce sells Trimcraft Aviation's stainless steel fuel tank screw kit for the C-172 as p/n 04-01003. These are MS27039 screws which are structural. As Jim has said, I would be concerned about galvanic corrosion if using these stainless MS27039C0808 and MS27039C0812 screws. You'll find it much cheaper to buy the screws à la carte rather than as a kit.

Really appreciate this! I didn't know anything about MS vs SS, so appreciate the explanation. I will order the MS versions - I'd rather replace the screws more often than galvanic corrosion.

[GAHorn]

….

Really appreciate this! I didn't know anything about MS vs SS, so appreciate the explanation. I will order the MS versions - I'd rather replace the screws more often than galvanic corrosion.

The term SS applies to the alloy used, such as Stainless Steel, …and in aviation hardware that is usually designated with a “C” in the PN.

The abbreviations of AN, MS, NAS are in reference to hardware quality standards. An Ad Hoc and unofficial explanation of AN/MS/NAS is…

The development of aircraft special hardware needs was identified by the army and the navy in the early part of last century, and a joint committee known as the "Army-Navy" aviation standards commitee worked out a mutually agreed standard which became known as the "Army/Navy" or "AN" standard. It described materials and fit specifications for aircraft hardware. As Aircraft became more sophisticated (and as the military services each became more involved in aviation) the standard was revised to include certain additional specialized fasteners, and a new standard known as the "Military Specification/Standard" or "MS" standard. As commercial aviation developed specialized needs for aircraft use, the "National Aerospace Standard" or "NAS" standard was defined.
Generally, AN bolts are approved for most applications, and most AN hardware also has "MS" definitions as well. The NAS hardware is usually more specialized, and almost always refers to hardware with higher strength materials and/or closer fit tolerances than ordinary AN/MS hardware. For that reason is is also more expensive.

Not the “official” definition…but …Hope this helps clarify.

The cautions against the use of “SS” hardware on aircraft is valid…but, in my personal opinion, unlikely to be a problem. The typical concerns are electrolytic or “galvanic” corrosion…. unlikely within the lifetime of your ownership of the airplane in most cases….. And the other concern is the use of powered hand-tools with “SS” screws, because it’s easier to damage the SS screw-slots than it is with “ordinary” AN or MS screws. (Once you’ve damaged the phillips-head of the screws they can be difficult to remove.)

Those who DO use “SS” or “Corrosion-resistant” (I.E. that’s what the “C” stands for in the PN) …. usually have no complaints…except from their A&Ps and IA’s because those guys spend their professional lives dealing with them after they’ve used their Makita or Milwaukee screw-guns stripping out those screw-heads. (I use the stainless “kits” I mentioned earlier on my airplane and have had no problems, and the reason I recommended the “kits” was because the excess amount of screws in those kits are helpful to already have on-hand if/when you do strip them.

A helpful little thing to reduce the “galvanic” corrosion issues is the use of nylon washers beneath the screw-heads when installing them. They are cheap and insulate the screw from it’s greatest electrolytic-contact-surface with the aluminum airplane and reduce the corrosion problem.
You can buy them from Spruce: If you use SS hardware I recommend them beneath the heads of the harware used on cowling and inspection cover applications…. I would not use the nylon washers in a structural application such as the fuel tank covers…. use “C” rated washers there if you use SS
MS27039C screwsl https://www.aircraftspruce.com/catalog/ ... ey=3010471

YMMV

[cessnut]

My initial reaction was due to the number of times I have found non-structural corrosion-resistant fasteners in aileron hinges and fuel tank covers. MS27039C screws have a tensile strength of 125000 psi and are an acceptable substitute. Whichever you decide, be sure to apply some corrosion inhibiting compound to the threads before you install them. I like to soak the screws in a ziploc bag with CorrosionX. The stainless screws will corrode with the nutplates in the spar over time. Simple fact. I have removed at least a dozen of these panels over the last couple years. Broken/stripped screws make the process a true pleasure.
Here's a fun tip for using nylon washers in non-structural applications. Use one size smaller washer(#8 on a #10 screw)and force it over the threads. The washer will be almost the exact diameter of the screw head after tightening, and they will not fall off and get lost when you remove the screws.