The Cessna 120-140 Association Forum

Hi,

Has anyone mapped the old Cessna parts numbers, e.g. those used in the C120/140 parts manual, to MS or AN numbers?

Example: pk76xz-8-8 used on the aileron bracket inspection panel. This is a machine screw.

I've seen similar part numbers used on the C-170.

Thanks, Chris

Actually, those screws (and most of the other screws in similar "inspection cover" applications) are not machine screws. They are called truss head type B sheet metal screws with a sort of sheet metal thread, but not tapered, and a blunt tip (type "B" as opposed to type "A"). They are intended to screw into Tinnerman nuts and the nut is designed to lock into the minor diameter of the thread. The "8-8" designation indicates it's a #8 screw 8/16 (1/2) inch long. You can order them here. Type "A" screws will not lock properly and tend to fall out.

They are available in steel or stainless. If you use stainless against aluminum you should use a nylon washer under the head to help prevent dissimilar metal corrosion (NAS1515H08L)

Type B PK screws are also used to hold the cowl and wing root fairings on.

They are "non-structural" and, to the best of my knowledge, have never had an AN, NAS or MS spec.

Thank you for the very informative answer. It looks like it goes with a Tinnerman A1348-8Z-1D.

I purchased the stainless Cessna 120 screw "kit" from Spruce. I'll check there first. And, find some nylon washers.

Keep 'em flying, Chris

riedener wrote: ↑Wed Jun 14, 2023 10:15 amIt looks like it goes with a Tinnerman A1348-8Z-1D.

Yes. There are a number of configurations: flat, u-shaped, j-shaped, etc.

Lots of good information here.

This is a great thread. I have yet to find anything but "type A" Truss head screws on my 1946-140. While type B are the proper parts over the years some lazy mechanics have switched them all out. Wing roots, cowling etc. You name it an its a type A.
Kind of makes me angry.

Cessna calls for a A1777-6Z-3 Tinnerman nut for the firewall heater vent mounting. However, that part seems to have disappeared in the aviation inventory. Neither Spruce nor Univair stock it.

I am having a difficult time matching the required hardware (1946) with modern designations.

As far as I can tell that's just a flat Tinnerman nut for a #6 PK screw. (not really flat, sort of curved...). NAS446-6-3 would work, but the -6 variant seems to be in very short supply...

Boeing lists A1777-6Z1, probably a different finish.

My 2012 copy of ECAS catalog also lists A1777-6Z-1D.

If you can't get the right part, a Tinnerman flush nut plate, A6191-6Z-1D, would probably work just fine, or go to machine screws and nuts.

Pretty sure I was able to get truss screws from Genuine Aircraft Hardware and maybe Spruce as well, as at one point I converted all the mixed A and B types to B throughout.

Aircraft Spruce has them here's what you order to get a #6 5/8 type B stainless screw:
Part# 04-00171 6X5/8-B-Tr-Ph-Stainless Steel Tapping Screw

Translation: #6 x 5/8" long type B truss head phillips stainless steel.