The chart
The clearance column is the one worth internalising: a rivet hole is deliberately two to four thousandths larger than the rivet. That gap lets the rivet go in without being driven home, and it closes when the rivet is upset and swells to fill the hole.
| Rivet size | AN dash | Shank Ø | Drill | Drill Ø | Clearance |
|---|---|---|---|---|---|
| 3/32" | -3 | 0.0938" | #40 | 0.0980" | +0.0042" |
| 1/8" | -4 | 0.1250" | #30 | 0.1285" | +0.0035" |
| 5/32" | -5 | 0.1563" | #21 | 0.1590" | +0.0027" |
| 3/16" | -6 | 0.1875" | #11 | 0.1910" | +0.0035" |
| 1/4" | -8 | 0.2500" | F | 0.2570" | +0.0070" |
Every drill in this table is the size given in Figure 4-90 of the FAA Airframe Handbook. AN dash numbers give diameter in thirty-seconds of an inch: -3 is 3/32", -4 is 4/32" = 1/8", and so on.
Alternates you will see quoted, and what they are for
Four other number drills turn up constantly in catalogues and forum threads. None of them is wrong — each has a job.
| Drill | Diameter | Relative to | What it is for |
|---|---|---|---|
| #41 | 0.0960" | 0.002" under #40 | Common shop-practice pilot ahead of #40. Not named as such in either FAA source. |
| #31 | 0.1200" | 0.005" under 1/8" | Same practice ahead of #30. Undersize even of the rivet, so never rivet into it. |
| #20 | 0.1610" | 0.002" over #21 | Quoted for 5/32" clecos. A cleco only has to fit the hole, not fill it to rivet tolerance. |
| #10 | 0.1935" | 0.0025" over #11 | Quoted for 3/16" clecos, for the same reason. |
Drill your rivet holes to the standard in the main chart. The cleco will still fit — that is the direction the tolerance runs.
The oversize repair sequence
When a hole is enlarged, elongated or damaged during rivet removal, the standard remedy is to go up one rivet size and re-drill to that rivet's drill. The sequence runs 3/32 → 1/8 → 5/32 → 3/16 → 1/4, and each step takes the drill from the row below it in the main chart.
Two things constrain this and both are easy to forget. First, edge distance is a function of diameter — going up a size increases the required edge distance by the same proportion, so a hole that was marginal on edge distance gets worse, not better. Second, the surrounding pattern was designed for the original size: pitch minimums scale with D as well.
In practice the oversize step is a legitimate and common technique, but it is a repair decision made against approved data, not a shop-floor reflex. Check the SRM. Some structures permit one oversize step and no more; some permit none.
Note also that an oversize repair changes the part callout. A hole taken from #30 to #21 now needs a 5/32" rivet — a different diameter code, a different length requirement, and a shop head 1.5 × 0.156" across rather than 1.5 × 0.125".
Drilling practice that actually affects the hole
Use a drill made for aluminum. A standard 118° jobber bit tends to grab and tear in thin soft alloy. Aircraft sheet metal bits are commonly ground at 135° with a split point, which centers without a punch and cuts rather than pushes.
Speed high, feed light. Aluminum likes a fast spindle and a gentle constant pressure. Leaning on the drill produces a triangular hole and a burr you will spend longer removing than you saved.
Back the sheet up. Drilling unsupported sheet lets it flex away from the bit and leaves a dished, oversized exit. A backing block behind the work is the difference between a round hole and an approximately round hole.
Deburr both sides, every hole. The burr on the exit side holds the sheets apart, and a joint riveted over burrs is a joint with a gap in it. This is the step most often skipped and most visible in the finished work.
Check the hole, not the drill. A worn or badly sharpened bit cuts oversize. If rivets are loose in freshly drilled holes, measure the hole before blaming the rivets.
Worked example
Match-drilling a 1/8" rivet line through two sheets of 0.032" 2024-T3.
- Pilot the run at #31 (0.1200") through both sheets clamped together — shop practice, see the note above.
- Cleco every third hole as you go — copper clecos for 1/8".
- Open each hole to final size with #30 (0.1285"), backing the sheet.
- The finished hole is 0.0035" larger than the 0.1250" rivet shank. That clearance is what lets the rivet drop in cleanly.
- Deburr both faces of both sheets, separate, clean, and reassemble to rivet.
- The rivet swells as it is driven and fills the 0.0035". A correctly driven rivet has no clearance left.
#31 then #30. The clearance is designed in, not a tolerance you are fighting.
Limits — when NOT to use this chart
Standard hole sizes for solid aluminum rivets in sheet metal.
- Approved data governs. The SRM, AMM or repair drawing specifies the hole. Where it differs from this chart, it wins.
- Blind and special fasteners have their own hole sizes. CherryMAX, Hi-Lok, lockbolts and Jo-Bolts are drilled and often reamed to the manufacturer's published dimensions, which are tighter and are not the drills in this chart.
- Interference-fit and reamed applications are different. Some structures call for a reamed hole to a tighter tolerance than a drill alone can hold. Drilling to size and stopping is not equivalent.
- Not for composites. Hole preparation in laminates involves different geometry, different tooling and delamination control at breakout.
- Oversize repair is a design decision. Going up a size changes edge distance and pitch requirements — see above.
- Drill wear defeats the chart. A worn bit cuts oversize regardless of what is stamped on it. Measure the hole on anything that matters.
Questions people actually ask
What drill size for an AN470AD4 rivet?
#30, which measures 0.1285". AN470AD4 is a 1/8" (4/32") diameter rivet, and 0.1285" gives the standard 0.0035" clearance.
What drill for a 3/32 rivet?
#40 (0.0980") as the final size. Where a pilot pass is used, #41 (0.0960") first.
Why is the hole bigger than the rivet?
So the rivet can be inserted without being forced. The clearance is two to four thousandths, and it disappears when the rivet is driven — the shank swells under the bucking bar and fills the hole completely. A rivet that fits tightly before driving cannot swell to fill anything.
Can I use a 1/8" drill instead of a #30?
No. A 1/8" drill measures 0.1250", identical to the rivet shank, leaving zero clearance. The rivet will not go in cleanly, and forcing it damages both the hole and the shank. #30 exists precisely because 1/8" is the wrong size for a 1/8" rivet hole.
What is the difference between #40 and #41?
Twenty ten-thousandths of an inch: #41 is 0.0960", #40 is 0.0980". #41 is the undersize pilot; #40 is the final size for a 3/32" rivet.
My rivets are loose in the holes. Wrong drill?
Possibly, but check the drill itself before the chart. A worn or asymmetrically sharpened bit cuts well over its nominal size. Measure a finished hole with pin gauges or callipers and compare against the drill Ø column above.
Sources
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Figure 4-90 — “Drill sizes for standard rivets” — the source of every drill and decimal in the main table above, plus drilling practice and deburring.
- FAA AC 43.13-1B CHG 1, Chapter 4 — hole preparation in the context of riveting. Note it does not carry the per-rivet drill table — that is the Handbook's.
- ANSI/ASME B94.11M number drill series — decimal diameters for number drills quoted in the tables above.
Where to buy drills
Aircraft sheet metal bits — 135° split point, cobalt or HSS — from both regional distributors.
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Want this as a printable?
Rivet sizes, drills, decimals, clearances and the oversize sequence on one page. The version that lives taped inside the drill index.