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Builders guide to safe aircraft materials

AN, MS hardware — rivets, bolts
and locking devices



Rev. 10a — page content was last expanded 22 January 2012
Page edited by RA-Aus member Dave Gardiner www.redlettuce.com.au January 2010
  
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In addition to the fittings discussed in module 11 the term 'aircraft hardware' also includes the fasteners used in aircraft assembly. In this and the next module of the Guide we look at rivets, threaded fasteners and locking devices.

Airframe fasteners are designed and manufactured to conform with long-established and proven standards for a system of fasteners. The standards most widely recognised are those originally defined by committees associated with the US military prior to and during World War 2 — the Army–Navy [AN] standards. The Military Standards [MS] followed — which superseded some AN standards and complemented others — and later came the National Aerospace Standards [NAS]; thus the common terms AN, MS and NAS. Those older US standards are in inches and fractions of inches only so there are few references to SI units on this page.


Some of the following material is noted as an extract from the FAA advisory circular AC 43.13-1B Chapter 7. The complete volume 'Acceptable methods, techniques, and practices — aircraft inspection and repair' (~ 650 pages and incorporating the 2001 changes) is available from the RA-Aus online shop for a reasonable price. It is bound together with the FAA advisory circular AC 43.13-2A 'Acceptable methods, techniques, and practices — aircraft alterations' (~ 100 pages).
12.1 Solid or driven rivets
The standard fastener for light aircraft constructed from sheet metal is the aluminium rivet; a recreational light aircraft built from aluminium sheet might use 6000 to 8000, maybe more. Rivets are used primarily to fasten aircraft skins to the substructure and to fabricate structural assemblies. Such joints are generally concerned with shear and tension loads. There are two rivet classes; the simple solid shank rivet, which is 'driven' using an air-operated rivet gun and a 'bucking bar' or 'dolly'; and the more complex 'blind' rivets requiring simpler (if the rivets are small diameter) installation tools to 'pull' them, but the tools may be unique to each pulled rivet manufacturer.

AN426 and AN470 rivets
There are quite a number of solid rivet types each made from a variety of materials — aluminium alloys, steel, corrosion-resistant steel, Inconel and Monel. However, apart from engine bay applications, there is generally only one solid rivet type of interest to light aircraft builders. That is the general structural use aluminium alloy 2117-T4 rivet generally with a 'universal' head (the upper rivet in the diagram) or possibly a 100° countersunk head (the lower rivet) — note the differing methods for measuring rivet length. The 2117-T4 material is galvanically compatible with the 6061 alloy and although such rivets have only about 80% of the strength of 2024-T3 rivets, the handling process is much simpler. Another type occasionally used in non-structural applicat