Structural shim of a Boeing aircraft

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I’m working on a repair of a Boeing aircraft. The repair requires solid shims (fillers) that meet the definition of a structural shim (per 737-300SRM 51-30-01). The issue I’m having is the specification requires that the structural shim is fastened to the repair component or the aircraft structure. I can’t not find definition on how the shim is to be fastened to those parts. Is the fasteners that are used to secure the shim to structure above and beyond the fasteners used in the repair? How many fasteners are required? What type and size? If anyone has any experience with this, I’d appreciate the insight.



  1. Shims in aerospace applications don’t have to be tapered.
  2. The term filler and shim are more or less interchangeable in most cases, especially with repairs. So the terminology can get a bit confusing.
  3. A structural shim, in this case would have to extend one row of fasteners further than the doubler for a typical application.

The main purpose of considering a shim structural is that by having it independently secured to the structure, it is not free to ‘float’ between the doubler and the repaired structure. That float is what causes fastener bending stresses that are difficult to account for (there’s analysis for it, but it’s not really well understood/researched so the analysis is very conservative).