Edge distance by rivet size
Minimum 2D for protruding-head rivets and 2½D for countersunk, with preferred values 1/16 in larger (Handbook Figure 4-79). The Handbook text also says edge distance should not be “less than 2 or more than 4 rivet diameters.”
| Rivet D | Min, protruding | Preferred, protruding | Min, countersunk | Preferred, countersunk | Max |
|---|---|---|---|---|---|
| 3/32" (0.094) | 0.188" | 0.250" | 0.234" | 0.297" | 0.375" |
| 1/8" (0.125) | 0.250" | 0.313" | 0.313" | 0.375" | 0.500" |
| 5/32" (0.156) | 0.313" | 0.375" | 0.391" | 0.453" | 0.625" |
| 3/16" (0.188) | 0.375" | 0.438" | 0.469" | 0.531" | 0.750" |
| 1/4" (0.250) | 0.500" | 0.563" | 0.625" | 0.688" | 1.000" |
D multiples and the +1/16 in step are from FAA-H-8083-31 Fig. 4-79 and p. 4-34; values are computed (rounded to 0.001 in). The same page's text calls “about 2½ rivet diameters” the recommended edge distance and Figure 4-81 shows 2 to 2½ D; see the table of where the sources differ below.
Minimum pitch — protruding head rivets
Figure 4-80 sets the minimum by the number of rows.
| Rivet D | Min, 1 and 3 rows (3D) | Preferred (+1/16) | Min, 2 rows (4D) | Preferred (+1/16) |
|---|---|---|---|---|
| 3/32" (0.094) | 0.281" | 0.344" | 0.375" | 0.438" |
| 1/8" (0.125) | 0.375" | 0.438" | 0.500" | 0.563" |
| 5/32" (0.156) | 0.469" | 0.531" | 0.625" | 0.688" |
| 3/16" (0.188) | 0.563" | 0.625" | 0.750" | 0.813" |
| 1/4" (0.250) | 0.750" | 0.813" | 1.000" | 1.063" |
FAA-H-8083-31 Fig. 4-80, p. 4-35; computed. AC 43.13-1B par. 4-57c(1) gives the same 3D for a single row.
Minimum pitch — countersunk head rivets
| Rivet D | Min, 1 and 3 rows (3½D) | Preferred (+1/16) | Min, 2 rows (4½D) | Preferred (+1/16) |
|---|---|---|---|---|
| 3/32" (0.094) | 0.328" | 0.391" | 0.422" | 0.484" |
| 1/8" (0.125) | 0.438" | 0.500" | 0.563" | 0.625" |
| 5/32" (0.156) | 0.547" | 0.609" | 0.703" | 0.766" |
| 3/16" (0.188) | 0.656" | 0.719" | 0.844" | 0.906" |
| 1/4" (0.250) | 0.875" | 0.938" | 1.125" | 1.188" |
FAA-H-8083-31 Fig. 4-80. The figure prints these as “3/1/2D” and “4/1/2D”, which reads as 3½D and 4½D; computed on that reading.
Usual pitch, transverse pitch and the largest pitch mentioned
The Handbook gives the average rivet pitch as 4 to 6 diameters, “as large as 10” in some cases. Transverse pitch is “usually 75 percent of the rivet pitch” and never below 2½ D.
| Rivet D | Usual pitch (4D–6D) | Transverse, smallest (2½D) | Transverse at 75% of 4D | Transverse at 75% of 6D | Largest pitch mentioned (10D) |
|---|---|---|---|---|---|
| 3/32" (0.094) | 0.375–0.563" | 0.234" | 0.281" | 0.422" | 0.938" |
| 1/8" (0.125) | 0.500–0.750" | 0.313" | 0.375" | 0.563" | 1.250" |
| 5/32" (0.156) | 0.625–0.938" | 0.391" | 0.469" | 0.703" | 1.563" |
| 3/16" (0.188) | 0.750–1.125" | 0.469" | 0.563" | 0.844" | 1.875" |
| 1/4" (0.250) | 1.000–1.500" | 0.625" | 0.750" | 1.125" | 2.500" |
FAA-H-8083-31 p. 4-35 and Fig. 4-81. 75% of 4D is 3D and 75% of 6D is 4½D. Computed.
What the sources say, and where they differ
| Rule | FAA-H-8083-31 | AC 43.13-1B | Note |
|---|---|---|---|
| Edge distance, minimum | 2D protruding, 2½D countersunk (Fig. 4-79, p. 4-34) | 2D, single row (par. 4-57c(1)); 2D in Fig. 4-5 | Agree. |
| Edge distance, preferred | Fig. 4-79: minimum + 1/16 in. Text: about 2½D. Fig. 4-81: 2 to 2½D | Not stated | The Handbook gives three different “preferred” figures. For a 1/8 in countersunk rivet Fig. 4-79 gives 0.375 in while the text gives about 0.313 in. |
| Edge distance, maximum | 4D | Not stated | Handbook only. |
| Pitch, minimum | Fig. 4-80: 3D (1 and 3 rows), 4D (2 rows), 3½D and 4½D countersunk. Text, p. 4-34: 3½D protruding, 4D flush. Text, p. 4-34 bullet: 3D | 3D, single row (par. 4-57c(1)). Fig. 4-5: 4D on the double-row splice, 3D on the triple-row | The Handbook disagrees with itself between p. 4-34 text and Fig. 4-80. Chart uses Fig. 4-80. |
| Pitch, usual | 4D to 6D, up to 10D (p. 4-35). Fig. 4-81: 6 to 8D | Fig. 4-5: 4D (double row) and 6D (triple row) | Different ranges; none is a limit. |
| Transverse pitch | 75% of pitch, never below 2½D. Bullet on p. 4-34: rows not closer than 2½D | Fig. 4-5: 4D between rows (double); 3D (triple) | AC figure is a splice drawing; the 4D and 3D are as read from it. |
Figure 4-5 values are read from the drawing: double row shows 2D edge, 4D pitch and 4D between rows; triple or multiple row shows 2D edge, 6D along a row and 3D between rows. AC par. 4-58 has no layout figures.
How the rules are used
Copy the original first. Both sources say the rivet spacing and edge distance should duplicate the original structure unless a structural problem is suspected (AC 4-57c). The Handbook says the same for most repairs: use the manufacturer's spacing around the damage and consult the SRM.
A new run. Find the edge distance at each end, then lay off the pitch between them. In a two-row layout, put the second row one transverse pitch from the first and stagger the rivets midway between those in the first row (Handbook p. 4-35).
Tubes. For rivets through a splice sleeve the Handbook gives a different rule: 4 to 7 rivet diameters apart if adjacent rivets are at right angles and 5 to 7 if parallel; the first rivet at least 2½D from the end of the sleeve.
Worked example — 3 in seam, 1/8 in protruding rivets, one row
A new 3.000 in seam in sheet metal. Use the preferred edge distance, and keep the pitch at or below 6D. Single row, so minimum pitch is 3D.
- D = 0.125 in. Preferred edge distance = 2D + 1/16 = 0.250 + 0.0625 = 0.313 in (table row 1/8).
- Distance between the two end rivets = 3.000 − 2 × 0.3125 = 2.375 in.
- Largest pitch wanted = 6D = 0.750 in. Spaces needed = 2.375 ÷ 0.750 = 3.17, so 4 spaces (round up).
- Pitch = 2.375 ÷ 4 = 0.594 in (4.75D). Minimum preferred pitch is 0.438 in, so it passes. That is 5 rivets.
- A second row would sit at least 2½D (0.313 in) away; at 75% of the 4D pitch, 0.375 in.
5 rivets at 0.594 in pitch, 0.313 in from each end. All the numbers come from the multiples in the tables above.
Questions people actually ask
What is the minimum edge distance for a rivet?
2 rivet diameters for a protruding head rivet and 2½ for a countersunk one, measured from the center of the hole (Handbook Fig. 4-79). AC 43.13-1B par. 4-57c gives 2D for a single row.
What is the minimum rivet spacing?
3D in a single row or triple row and 4D in a double row of protruding head rivets; 3½D and 4½D for countersunk (Fig. 4-80). Text on p. 4-34 gives 3½D and 4D, which does not match. Use the SRM or drawing if in doubt.
What is transverse pitch?
The perpendicular distance between rows of rivets. Usually 75% of the rivet pitch and never less than 2½D (Handbook p. 4-35).
What does the 1/16 in added to the minimum mean?
It is the Handbook's “preferred” value: if spacing is at least 1/16 in larger than the minimum, the hole can be oversized later without breaking the minimum.
Is there a maximum edge distance?
The Handbook says not more than 4D. The AC does not give a maximum.
Limits — when NOT to use this chart
These are minimum rules for solid aluminum rivets in sheet metal, not authority for a given repair.
- The aircraft's manual governs. An SRM, repair drawing or approved data overrides every number here.
- Match the existing pattern. On a patch that ties into structure, rivet where the original rivets are.
- Blind and special fasteners (Cherry, Hi-Lok, lockbolts) have their own edge distance and spacing in the manufacturer's data.
- Composites use different rules. The Handbook's composite repair section (Chapter 7) gives four diameters from existing fasteners and three diameters edge distance for its pilot holes, not the 2D here.
- The pitch figures are minimums, not targets. Pressure skins and fuel tank boundaries are driven by sealing and fatigue.
Sources
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 4, pp. 4-34 and 4-35, Figures 4-79, 4-80 and 4-81 — edge distance minimum, preferred and maximum; rivet pitch by number of rows and head type; transverse pitch at 75% of pitch with a 2½D floor; the +1/16 in preferred step; tube splice spacing.
- FAA AC 43.13-1B CHG 1, Chapter 4, par. 4-57c and Figure 4-5 (p. 4-20) — the 2D edge distance and 3D spacing for a single row; double and multiple row minimums shown only in Figure 4-5. Par. 4-58 carries no layout figures.