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Replacement Screws for Phillips

macrafic

Well Known Member
I agree with those who are looking for alternative screws to the AN-509 Phillip screws. However, a bit of caution is in order, so that you know the difference between a structural and a non-structural application. Van's plans do not point this out. Here is the reply I got from MicroFasteners when I asked about their screws. Microfasteners is the brand that has shown up quite a bit on various RV forums:

"Our stainless steel 100 degree flat head torx drive screws are all intended
to replace the cross recessed screws of NASM24693 (which has superseded AN507) covering non-structural screws. Their tensile strength is 85,000 psi minimum, same as the requirement for structural screws of NASM24694 (which has superseded AN509,) so the tensile strength for 8-32 screws is 1190 lbs, minimum. However their intended use is nonstructural and the grip length requirement of the structural screw spec is not met.

We emphasize that these are not mil spec screws; first no testing has been done to verify that, apart from the different drive, they meet the
requirements of either of the specs listed above, and second there is no mil spec covering these screws, to the best of our knowledge.

We don't have the AN509 spec, but the superseding NASM spec lists parts of three different compositions and hence strengths: low alloy steel at 125,000 psi, aluminum alloy at 62,000 psi and corrosion resistant (stainless) steel at 85,000 psi. Our parts are the latter. Please don't use them where the 125,000 psi parts are specified."
 
Hmmmmm

WOW! I got the idea to get these s/s screws from the guy in the next hangar. He has them all over his Lancair.

Has anybody been using these on an RV???
Cheers, Pete
 
Yes, they are quite common. I use them for many non-structural items such as attaching wingtips, fairings, etc. I really like them.
 
Thinking about it

In thinking about the airframe, I can't put my finger on any specific part that I'd consider structural that uses these screws. Also, I have buggered up the head of many of these screws, so they are relatively soft. (509's).

I bought SS screws from Spruce for my fuel tanks, wing tips, fairings and wheel pants. These are for final assembly after paint.
 
Wing tip attachment

william weesner said:
how can a wing tip not be structural...if lost the drag would be more causing some issues and what if it only came loose at the front and pivoted out and locked the ailerons...yes i am sure the screws are surely stronger than pop tivets but i get the willys when someone says non structural refferring to a part that is 1/4" away from interfering with my flight controls.
A good point. I too feel the screws are likely to be stronger than the pop rivets. Experience with many screw attached wingtips on RV's has been good I think - at least I haven't heard of problems. Has anybody else? I'm planning to use the SS screws on the wingtips. What are thoughts on screws holding floor sections, seat ramps etc? Bill
 
Fuel tank attachment

szicree said:
The fuel tank attach is definitely "structural".

The fuel tank main structure attachment point on a 7 is the "Z" brackets on the back. Obviously the screws are important but not the main issue. The SS have to be stronger than the standard screws.

Regarding the wing tips, with so many screws holding them on, I'm confident the SS are more than adequate.

I think we're trying to pole vault a mouse turd on this issue. I think we can use SS with confidence.
 
SS Screws

The torx screws from Microfasteners are all stainless. Now, I'm no paint expert, but I understand that paint does not adhere well to stainless hardware. For that reason I used regular cad plated 507s for my tanks, and stainless torx just about everywhere else.
 
RV7Guy said:
The fuel tank main structure attachment point on a 7 is the "Z" brackets on the back. Obviously the screws are important but not the main issue. The SS have to be stronger than the standard screws.

Regarding the wing tips, with so many screws holding them on, I'm confident the SS are more than adequate.

I think we're trying to pole vault a mouse turd on this issue. I think we can use SS with confidence.

I'm no engineer and don't know about the particulars of the 7 wing, but I can tell you that the wing is a whole lot less rigid with all of those screws removed. My wing is on the plane and with the tank removed the whole wing is noticably more flexible. I take this to mean that on my 4 the tank screws are a structural element. Regarding the strength of the SS, didn't the beginning of this thread start with a statement from the manufacturer saying that their product does not have the tensile strength of the steel part? I'm not saying these screws are unsafe and I'm using them for all my fiberglass, but on the tanks I'm just not sure. I'd love to hear from some engineering types on this one.
 
I haven't really thought through this too much but it's my intuition that part of the advantage of a nested dimples is that it loads the screw in tension as well as shear (in general, you don't really want to load screws/bolts in shear without a faily close tolerance hole). In order for the joint to shear it must also pull apart because the dimple is redirecting the force. Without that, I don't think just sticking screws into these huge countersunk holes would work very well at all.

My 15 second analysis of what's going on (don't take it to the bank, I'm probably wrong). Someone should just call Van's and ask.

If you use a drop of that screw grip stuff that Avery sells it makes it much easier to torque the phillips screws without stripping them.
 
I called Van's

I called Van's. I won't mention who I talked to because of the final comments from this person. (Great guy by the way, very helpful.)

He said Van's replaces all the hardware in company planes with SS. It is fine in all applications especially in areas where you are contacting painted areas.

I am wrapping up paint now and painted the tanks separately. I will be using SS on the tanks for the above reason.

Oh yeah, the most important comment. He said everybody overthinks these things and should spend more time building and way from the keyboard!!!!

Gotta agree with that one. Lunch over, back to painting.
 
RV7Guy said:
I am wrapping up paint now and painted the tanks separately. I will be using SS on the tanks for the above reason.

Oh yeah, the most important comment. He said everybody overthinks these things and should spend more time building and way from the keyboard!!!!

Gotta agree with that one. Lunch over, back to painting.

Haha, I gotta agree with that. I suspect that I'll do the same as you and use those ss torx fasteners everywhere. I used em on my tips and they totally spoiled me for those crappy phillips type. Good to hear that our fearless leader approves.
 
torx/ss screws

I am using the Microfasteners/torx everywhere that is not painted: wingtip attach, fairings in empennage and gear legs, inspection plates. I continue with the Milspec phillips at tank attach and (although probably not necessary) canopy-to-fuse attach on the tipper. (over the roll bar I am torx only). Somewhere in the middleground: I use torx to attach floors and internal covers like hi pressure fuel pump covers. Just one more opinion...
Len
N72ML, OSH if very, very, fortunate. Dual Cheltons all glass
 
I've looked for "torx" can't find... is this their version of "torx"

100 Deg Flat Head 6 Lobe Drive

M
 
Where to buy?

LAL said:
I am using the Microfasteners/torx everywhere that is not painted: wingtip attach, fairings in empennage and gear legs, inspection plates. I continue with the Milspec phillips at tank attach and (although probably not necessary) canopy-to-fuse attach on the tipper. (over the roll bar I am torx only). Somewhere in the middleground: I use torx to attach floors and internal covers like hi pressure fuel pump covers. Just one more opinion...
Len
N72ML, OSH if very, very, fortunate. Dual Cheltons all glass



Where's the best (read: cheapest) place to buy these?
 
SS: Torx vs Phillips head

szicree said:
Haha, I gotta agree with that. I suspect that I'll do the same as you and use those ss torx fasteners everywhere. I used em on my tips and they totally spoiled me for those crappy phillips type. Good to hear that our fearless leader approves.

A couple of thoughts - be careful to differentiate between SS phillips type screws and SS torx screws. I believe it is the case that the head strength on the torx is significantly less than for phillips, owing to less material between the cone of the head and the torx well. Maybe this isn't the case any more, but it was discussed at length a number of years ago on another list. So, when Van's representatives say SS is ok, be sure they know the subtleties between SS phillips and SS torx.

The other thought relates to this ongoing problem people seem to have with phillips screws. I have hundreds of SS phillips screws all over my plane, and some of them have been in and out many, many times. I am still waiting to strip one when a decent driver is used. I have only replaced screws because of losing them (Pete, "loosing" for you :p ). Throw away any screwdrivers you have that don't use inserts, and keep the driver aligned, and you shouldn't have any problems.
 
Source for SS Allen Head Drive

For those who may want allen head drive SS screws, two sources are:

http://www.fastener-express.com/index.asp?PageAction=VIEWCATS&Category=207

or

http://www.boltdepot.com/socket-products.aspx

Both companies list them as Button Head socket screws and are quick shippers. Bolt Depot is a little more expensive, but they have longer screws in the button head design.

I like the Allen head screw simpley because I'm less likely to lost the multitude of allen wrenches that I have :D
 
Another tip for solving "stripped phillips screw" problems. Just place a touch of
valve grinding compound on the tip of your screwdriver and you will see amazing results. Also a phillips screw driver tip that has serration's on it will help.
 
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