(JDupre5762) wrote in message
...
MS 24694 are flush type structural screws and are available in
stainless (MS 24694C). Spruce, Chief, Wicks, and many others have
them.

That may well be true but when I spoke to D&D supply a couple of years ago
they
told me that the stainless flush screws were not strong enough for the
application and they would not sell them in thier Piper fuel tank kits. I
suppose that lots of things can change in two years. I will call them
tomorrow
and ask again.

John Dupre'

John,
MS 24694C screws are 300 series stainless with an ultimate strength of
85,000 psi. Typical non-structural machine screws have tensile
strengths of 55-60,000 psi. Most steel structural screws (MS 27039, AN
525, MS 24694) have tensile strengths of 125,000 psi. The MS 24694C
are classified as structural since they have an unthreaded shank
portion where any shear load is carried. This unthreaded portion is
critical to any structural screw as having threads in shear is a BIG
no-no. If you need to have stronger screws that 85 ksi., then they are
made but I don't know who sells them. The 85 ksi screws are stronger
than the 2024-T3 aluminum they are mounted in for any thickness up to
.120 in. for the thinnest flange that the tanks or wing section may
have (not the total thickness, for a #10 size screw which is I think
the size used in the tanks). If you want to look for them, either NAS
1221E or NAS 8703 are 160,000 psi corrosion resistant alloy, flush
structural screws. Gen aircraft hardware does not sell them, but if
you call them they may know who does.


I spoke to D&D Aircraft Supply today. What they told me is that they try to
guarrantee that their stainless screws have the same or better strength as the
original cadmium plated steel structural screws. As stated above the type of
stainless steel used in MS 24694 screws leaves the screw actually weaker than
the original cadmium plated variety. D&D says that the stainless variety may
well be strong enough and Piper might admit that but D&D's decision is to
market replacement stainless kits that are known to be a direct replacement for
the original cad plated steel hardware as specified by Piper, or Cessna etc.

John Dupre'