The calculator
Runs in your browser. Inches or millimetres at the top.
The rules it applies
AC 43.13-1B paragraph 4-57b: “Replace rivets with those of the same size and strength whenever possible. If the rivet hole becomes enlarged, deformed, or otherwise damaged; drill or ream the hole for the next larger size rivet. However, make sure that the edge distance and spacing is not less than minimums listed in the next paragraph.” Those minimums are 2D edge distance and 3D pitch for a single row.
The trap: the minimums scale with the new rivet. Going from 1/8 to 5/32 in moves the minimum edge distance from 0.250 to 0.313 in. A hole that was legal at 1/8 in can fail at 5/32 in.
The 2117 substitution. The same paragraph allows 2017 rivets of 3/16 in or less, and 2024 rivets of 5/32 in or less, to be replaced with 2117 rivets for general repairs, “provided the replacement rivets are 1/32 inch greater in diameter”. The calculator names that option when it applies.
The size is chosen as the smallest standard rivet whose drill is at least the hole you measured, using the drill sizes from the rivet drill chart.
Worked example
A 1/8 in AD rivet drilled out; the hole now measures 0.140 in. Its centre is 0.32 in from the edge and 0.50 in from the next rivet.
- 0.140 in is larger than the #30 drill (0.1285 in). Next size: 5/32 in, #21 drill (0.159 in).
- Edge distance 0.32 in ≥ 2 × 0.156 = 0.313 in: passes, by 0.007 in.
- Pitch 0.50 in ≥ 3 × 0.156 = 0.469 in: passes.
Drill #21 and fit an MS20470AD5. With the hole centre at 0.30 in from the edge, the same job would need a repair design.
Limits — when NOT to use this
- Duplicate the original first. AC 4-57c: unless structural deficiencies are suspected, edge distance and spacing should duplicate the original structure. The 2D and 3D figures are the floor the AC gives for when they are.
- Approved data governs. The SRM may call for oversize rivets, a specific fastener, or a repair, and in pressurized or primary structure it usually does.
- Solid rivets only. Blind fasteners have their own oversize series and hole limits.
- A row of oversize rivets is not a series of single replacements; ask for a repair design.
- Measure from the hole centre, with the hole drilled to the new size in mind.
Questions people actually ask
Why not just a bigger rivet everywhere?
Because the edge distance and pitch minimums grow with the diameter. The AC allows the next size only where they still hold.
Can I replace a 2024 DD rivet with an AD one?
For general repairs, a 2024 rivet of 5/32 in or less may be replaced by a 2117 rivet 1/32 in larger (AC 4-57b). The larger rivet must still meet edge distance and pitch.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 4, par. 4-57b and 4-57c — next larger size for an enlarged hole, edge distance and spacing minimums, no weaker replacement, and the 2117 substitution at +1/32 in.
- Rivet drill size chart — #40, #30, #21, #11 and F drills for 3/32 to 1/4 in rivets.