AN screw terminology

This is a good reference for standard aircraft hardware.

On Page 108 you’ll find your AN525 screws:

AN525 832R9 is an #8-32 Phillips head machine screw with integral washer, 9/16" long with 5/32" grip length. Rated material strength is 125 ksi. A graphic is provided.

AN526 832R8 is an #8-32 truss head machine screw, 9/16" long. Rated material strength is 55 ksi. A graphic is provided.

On Page 106 are AN 960 washers:

AN960 PD8L is an anodized 2024 AL (aluminum) flat washer to fit a #8 screw. Graphic and dimensions are provided.

LN9025 is I believe a DIN (German national) numbering system for flat washers, but there is an additional suffix required to describe the size. I’m guessing your old Bölkow parts book is communicating that either an AN960 or LN9025 washer is acceptable.

I have tried sometimes to get some info on the German LN standard for aircraft hardware, but gave up each time It really would be nice to have the standard and parts readily available as it is standard metric DIN parts, only with a higher standard for “failure” rate.

Except that the AN (Army / Navy) stuff isn’t metric, it is inch-based (imperial?) – as Silvaire explained above :) The DIN / LN probably is :)

FWIW, many, if not all, AN specs have been superceeded by a MIL spec:

AN507 is MS24693 (cadmium plated) and MS24693C (stainless) – non-structural
AN509 is MS24694 (cadmium plated) and MS24694C (stainless) – structural

AN515 and AN526 are MS35206, I think.

AircraftSpruce have them all, I recently spent way too much money buying a mini spares collection.

I’ve also found the site everyspec.com useful.

tmo wrote:

AircraftSpruce have them all, I recently spent way too much money buying a mini spares collection.

I have spent tons of money on hardware from ACS AN bolts are nice, but AN (MS) screws are complete junk compared with standard metric screws from good (professional) hardware stores. Poor quality heads, poor threads. If I had some place to get LN stuff at an obtainable price, I would, especially screws.

Do tell, are the metric LN screws really direct replacements for the imperial AN/MS screws? Genuine question, as I am sure I’ll be missing a size or three anyway, and getting stuff from Spruce takes time and too much money. Or are you able to use them because you’re building from scratch, and can use whatever you want?

They are different threads, although a monkey is well capable of forcing one into another with enough force

American GA aircraft screws (the small ones, especially) are coarser pitch than metric screws of same diameter. The top and bottom are M3 and M4 respectively while the middle one is a UNC (unified coarse) thread:

There is also UNF (unified fine) which is finer, and used for bigger bolts in US aircraft. Upper is M6 and the lower is UNF

BUT if you happen to be replacing both ends (the bolt and the nut, or the bolt and the nutplate) then obviously metric can be used instead of UNC/UNF, in uncritical areas.

I wouldn’t say the US fasteners are of worse quality. It depends on which ones you buy. I have a box full of precision standard aircraft bolts…

Spruce has a German distributor called Sandelving, trading/as Aircraft Spruce EU, but there have been reports of extremely slow deliveries recently. I phoned them up to check out certain stories which they flatly denied…

The AN/MS system is wonderful for controlling pricing of aircraft fasteners and preventing ripoffs like this where a fairly ordinary M4 screw is sold for 100x more than the right price. BTW I still have stock of them Europe failed to create a system of “standard aircraft fasteners” and this enables these practices to continue – especially in aviation where most owners are bent over the barrel of their maintenance company which demands “paperwork”.

Don’t get me started on fasteners. Everything on mine is Whitworth, except the engine and brakes which are all AN/MS, and all the fuel pipes are BSPP except where it finally connects to the engine… fortunately, LAS seem to stock a tonne of Whitworth hardware, and BSPP/BSPT is still widely used on the hydraulics on things like tractors.

Aaaah Whitworth. What about BSF (British Standard Fine)? Beautiful fine threads. The days when engineers were men, had oily hands, and life was real

Yes LAS Aero is a good source for fasteners although they keep a limited range, and very little metric (predictably since there are no “standard” parts).

Do tell, are the metric LN screws really direct replacements for the imperial AN/MS screws? Genuine question, as I am sure I’ll be missing a size or three anyway, and getting stuff from Spruce takes time and too much money. Or are you able to use them because you’re building from scratch, and can use whatever you want?

As Peter said. For bolts you can use “whatever you want” but AN bolts are OK anyway, and I have found no place to get LN bolts. Lots of ULs use LN bolts, or DIN NL or whatever it is called, in critical places like wing bolts for instance, but where do they get them?

For most screws you have to make the threads anyway, or use nutplates. These things are usually not part of any critical structure, and if they are, they are usually used as a, more practical, substitute for rivets. Any steel screw is (much) stronger than a rivet regardless. In those cases I would rather use metric screws.