Rivet pilot and final drills (FAA-H-8083-31, Figure 4-90)
The Handbook's figure lists a pilot and a final drill for each common rivet diameter. The pilot is the fractional drill of the rivet's own size; the final is the clearance drill. Clearance is the final drill minus the rivet's shank diameter.
| Rivet | Rivet Ø | Pilot drill | Final drill | Final mm | Clearance |
|---|---|---|---|---|---|
| 3/32" | 0.0938" | 3/32" (0.0937) | #40 (0.0980") | 2.49 | +0.0042" |
| 1/8" | 0.1250" | 1/8" (0.125) | #30 (0.1285") | 3.26 | +0.0035" |
| 5/32" | 0.1563" | 5/32" (0.1562) | #21 (0.1590") | 4.04 | +0.0027" |
| 3/16" | 0.1875" | 3/16" (0.1875) | #11 (0.1910") | 4.85 | +0.0035" |
| 1/4" | 0.2500" | 1/4" (0.250) | F (0.2570") | 6.53 | +0.0070" |
Pilot and final drills as printed in Figure 4-90. Clearance and the mm column are arithmetic (inches × 25.4, shank decimals rounded to four places). The Handbook text says rivet hole drills should be “the smallest size that permits easy insertion of the rivet, approximately 0.003-inch greater than the largest tolerance of the shank diameter.”
Number drills, #1 to #40
A bigger number is a smaller drill. #1 is 0.2280 in and #80 is 0.0135 in. The four you will use most on rivets are in bold in the rivet table above: #40, #30, #21 and #11.
| Drill | Decimal (in) | mm |
|---|---|---|
| #1 | 0.2280" | 5.79 |
| #2 | 0.2210" | 5.61 |
| #3 | 0.2130" | 5.41 |
| #4 | 0.2090" | 5.31 |
| #5 | 0.2055" | 5.22 |
| #6 | 0.2040" | 5.18 |
| #7 | 0.2010" | 5.11 |
| #8 | 0.1990" | 5.05 |
| #9 | 0.1960" | 4.98 |
| #10 | 0.1935" | 4.91 |
| #11 | 0.1910" | 4.85 |
| #12 | 0.1890" | 4.80 |
| #13 | 0.1850" | 4.70 |
| #14 | 0.1820" | 4.62 |
| Drill | Decimal (in) | mm |
|---|---|---|
| #15 | 0.1800" | 4.57 |
| #16 | 0.1770" | 4.50 |
| #17 | 0.1730" | 4.39 |
| #18 | 0.1695" | 4.31 |
| #19 | 0.1660" | 4.22 |
| #20 | 0.1610" | 4.09 |
| #21 | 0.1590" | 4.04 |
| #22 | 0.1570" | 3.99 |
| #23 | 0.1540" | 3.91 |
| #24 | 0.1520" | 3.86 |
| #25 | 0.1495" | 3.80 |
| #26 | 0.1470" | 3.73 |
| #27 | 0.1440" | 3.66 |
| #28 | 0.1405" | 3.57 |
| Drill | Decimal (in) | mm |
|---|---|---|
| #29 | 0.1360" | 3.45 |
| #30 | 0.1285" | 3.26 |
| #31 | 0.1200" | 3.05 |
| #32 | 0.1160" | 2.95 |
| #33 | 0.1130" | 2.87 |
| #34 | 0.1110" | 2.82 |
| #35 | 0.1100" | 2.79 |
| #36 | 0.1065" | 2.71 |
| #37 | 0.1040" | 2.64 |
| #38 | 0.1015" | 2.58 |
| #39 | 0.0995" | 2.53 |
| #40 | 0.0980" | 2.49 |
Number drills, #41 to #80
A bigger number is a smaller drill. #1 is 0.2280 in and #80 is 0.0135 in. The four you will use most on rivets are in bold in the rivet table above: #40, #30, #21 and #11.
| Drill | Decimal (in) | mm |
|---|---|---|
| #41 | 0.0960" | 2.44 |
| #42 | 0.0935" | 2.37 |
| #43 | 0.0890" | 2.26 |
| #44 | 0.0860" | 2.18 |
| #45 | 0.0820" | 2.08 |
| #46 | 0.0810" | 2.06 |
| #47 | 0.0785" | 1.99 |
| #48 | 0.0760" | 1.93 |
| #49 | 0.0730" | 1.85 |
| #50 | 0.0700" | 1.78 |
| #51 | 0.0670" | 1.70 |
| #52 | 0.0635" | 1.61 |
| #53 | 0.0595" | 1.51 |
| #54 | 0.0550" | 1.40 |
| Drill | Decimal (in) | mm |
|---|---|---|
| #55 | 0.0520" | 1.32 |
| #56 | 0.0465" | 1.18 |
| #57 | 0.0430" | 1.09 |
| #58 | 0.0420" | 1.07 |
| #59 | 0.0410" | 1.04 |
| #60 | 0.0400" | 1.02 |
| #61 | 0.0390" | 0.99 |
| #62 | 0.0380" | 0.97 |
| #63 | 0.0370" | 0.94 |
| #64 | 0.0360" | 0.91 |
| #65 | 0.0350" | 0.89 |
| #66 | 0.0330" | 0.84 |
| #67 | 0.0320" | 0.81 |
| #68 | 0.0310" | 0.79 |
| Drill | Decimal (in) | mm |
|---|---|---|
| #69 | 0.0293" | 0.74 |
| #70 | 0.0280" | 0.71 |
| #71 | 0.0260" | 0.66 |
| #72 | 0.0250" | 0.64 |
| #73 | 0.0240" | 0.61 |
| #74 | 0.0225" | 0.57 |
| #75 | 0.0210" | 0.53 |
| #76 | 0.0200" | 0.51 |
| #77 | 0.0180" | 0.46 |
| #78 | 0.0160" | 0.41 |
| #79 | 0.0145" | 0.37 |
| #80 | 0.0135" | 0.34 |
Decimals as printed in Figure 4-47; millimetres are the inch value × 25.4.
Letter drills, A to Z
Letter drills start where number drills end: A (0.2340 in) is larger than #1 (0.2280 in). Z is 0.4130 in.
| Drill | Decimal (in) | mm |
|---|---|---|
| A | 0.2340" | 5.94 |
| B | 0.2380" | 6.05 |
| C | 0.2420" | 6.15 |
| D | 0.2460" | 6.25 |
| E | 0.2500" | 6.35 |
| F | 0.2570" | 6.53 |
| G | 0.2610" | 6.63 |
| H | 0.2660" | 6.76 |
| I | 0.2720" | 6.91 |
| J | 0.2770" | 7.04 |
| K | 0.2810" | 7.14 |
| L | 0.2900" | 7.37 |
| M | 0.2950" | 7.49 |
| Drill | Decimal (in) | mm |
|---|---|---|
| N | 0.3020" | 7.67 |
| O | 0.3160" | 8.03 |
| P | 0.3230" | 8.20 |
| Q | 0.3320" | 8.43 |
| R | 0.3390" | 8.61 |
| S | 0.3480" | 8.84 |
| T | 0.3580" | 9.09 |
| U | 0.3680" | 9.35 |
| V | 0.3770" | 9.58 |
| W | 0.3860" | 9.80 |
| X | 0.3970" | 10.08 |
| Y | 0.4040" | 10.26 |
| Z | 0.4130" | 10.49 |
Decimals as printed in Figure 4-47. E and 1/4 in are both 0.2500 in.
Fractional drills, 1/64 to 1/2 in by 64ths
| Drill | Decimal (in) | mm |
|---|---|---|
| 1/64" | 0.0156" | 0.40 |
| 1/32" | 0.0312" | 0.79 |
| 3/64" | 0.0468" | 1.19 |
| 1/16" | 0.0625" | 1.59 |
| 5/64" | 0.0781" | 1.98 |
| 3/32" | 0.0937" | 2.38 |
| 7/64" | 0.1093" | 2.78 |
| 1/8" | 0.1250" | 3.18 |
| 9/64" | 0.1406" | 3.57 |
| 5/32" | 0.1562" | 3.97 |
| 11/64" | 0.1718" | 4.36 |
| 3/16" | 0.1875" | 4.76 |
| 13/64" | 0.2031" | 5.16 |
| 7/32" | 0.2187" | 5.55 |
| 15/64" | 0.2343" | 5.95 |
| 1/4" | 0.2500" | 6.35 |
| Drill | Decimal (in) | mm |
|---|---|---|
| 17/64" | 0.2656" | 6.75 |
| 9/32" | 0.2812" | 7.14 |
| 19/64" | 0.2968" | 7.54 |
| 5/16" | 0.3125" | 7.94 |
| 21/64" | 0.3281" | 8.33 |
| 11/32" | 0.3437" | 8.73 |
| 23/64" | 0.3593" | 9.13 |
| 3/8" | 0.3750" | 9.53 |
| 25/64" | 0.3906" | 9.92 |
| 13/32" | 0.4062" | 10.32 |
| 27/64" | 0.4219" | 10.72 |
| 7/16" | 0.4375" | 11.11 |
| 29/64" | 0.4531" | 11.51 |
| 15/32" | 0.4687" | 11.90 |
| 31/64" | 0.4844" | 12.30 |
| 1/2" | 0.5000" | 12.70 |
Decimals as printed in Figure 4-47, which truncates some of them rather than rounding (3/32 is exactly 0.09375 but is printed 0.0937). The Handbook prints 1/64 as “1/54” and 39/64 as “39/84”; the typos are corrected here. The Handbook chart continues to 1 in.
Which series, and in what order
Drills come in three series that interleave: number (#80 up to #1), letter (A up to Z) and fractional (1/64 in steps). Sheet metal work lives mostly in the number series, because rivet holes are small and need small steps. The Handbook says drill diameters “are grouped by three size standards: number, letter, and fractional.”
A fractional drill is rarely the right drill for a rivet. A 1/8 in drill is exactly 0.1250 in, the same as a 1/8 in rivet shank, so the rivet has no clearance. That is why Figure 4-90 uses the fractional size only as the pilot and a number drill as the final.
Pilot drills and holes above 3/16 in
The Handbook describes the procedure for holes larger than 3/16 in in sheet metal as: “drill a pilot hole with a No. 40 or No. 30 drill bit and then to oversize with a larger drill bit to the correct size.” (Chapter 4, step drill bits, p. 4-17.) On rivet holes it also says to drill “a slightly undersized hole (pilot hole)” and ream it with the proper twist drill (p. 4-40).
Where the sources differ: Figure 4-90 shows the fractional drill as the pilot for each rivet size, while the text names a No. 40 or No. 30 as the pilot for larger holes. The common shop habit of #41 before #40 or #31 before #30 is in neither source; see the rivet drill chart.
Worked example — 5/32 in rivet
A 5/32 in rivet line in sheet metal. Look the sizes up in the rivet table and the number table.
- Pilot: 5/32 in (0.1562 in as printed in Figure 4-90). Final: #21 (0.1590 in).
- Clearance: 0.1590 − 0.1563 = 0.0027 in.
- In millimetres: 0.1590 × 25.4 = 4.04 mm.
- Deburr both sides after drilling, as the Handbook says, before riveting.
Final drill #21, 0.1590 in, 4.04 mm. Check the drawing or SRM, which can call for a different hole.
Questions people actually ask
What drill size for a 1/8 inch rivet?
#30, 0.1285 in (3.26 mm). Figure 4-90 gives a 1/8 in pilot (0.125 in) and a #30 final.
Is a #1 drill bigger than a #60?
Yes. #1 is 0.2280 in and #60 is 0.0400 in. Number drills get smaller as the number goes up.
Is an A drill bigger than a #1?
Yes, A is 0.2340 in and #1 is 0.2280 in. Letters start where numbers stop.
What size is a #40 drill in millimetres?
0.0980 in × 25.4 = 2.49 mm.
Why is the rivet hole drill bigger than the rivet?
For clearance. Figure 4-90 gives 0.0027 in to 0.0042 in on the four smaller rivets and 0.0070 in on the 1/4 in rivet with an F drill. The rivet swells when driven and fills the hole.
Limits — when NOT to use this chart
Decimal sizes are for the drill itself. The hole a drill cuts can be larger, and the hole a drawing calls for is often not the drill size.
- The drawing or SRM governs hole size. The Handbook says hole sizes for other fasteners are found on work documents, prints or in manuals.
- Blind rivets, Hi-Lok and lockbolts have their own hole and reaming sizes. Do not take them from the rivet table.
- Bolt holes follow AC 43.13-1B par. 7-39, the first-lettered drill larger than the bolt, except in close-fit or reamed holes. Use the bolt hole calculator.
- A worn bit cuts oversize. Measure the hole, not the bit.
- Metric drills are not on this chart. The mm column converts the inch drill; it does not name a metric drill that is equal.
Sources
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 4, Figure 4-47 (p. 4-18) — “Drill sizes and decimal equivalents”: every decimal in the number, letter and fractional tables. The decimals are the Handbook's printed values; the two typos noted above are corrected.
- FAA-H-8083-31, Airframe, Volume 1, Chapter 4, Figure 4-90 (p. 4-40) and p. 4-17 — pilot and final drills for 3/32 to 1/4 in rivets, the 0.003 in clearance rule, the pilot-hole procedure and the No. 40 / No. 30 pilot for holes above 3/16 in.
- FAA AC 43.13-1B CHG 1, Chapter 7, par. 7-39 — bolt fit and the first-lettered drill rule referred to in the limits.