Fine thread series (in-lb)
Thread size is nominal diameter and threads per inch, for example 1/4-28. An install value is a range; a max value is a single limit that is not to be exceeded.
| Thread size | Install: tension nut | Install: shear nut | Max: tension nut | Max: shear nut |
|---|---|---|---|---|
| 8-36 | 12–15 | 7–9 | 20 | 12 |
| 10-32 | 20–25 | 12–15 | 40 | 25 |
| 1/4-28 | 50–70 | 30–40 | 100 | 60 |
| 5/16-24 | 100–140 | 60–85 | 225 | 140 |
| 3/8-24 | 160–190 | 95–110 | 390 | 240 |
| 7/16-20 | 450–500 | 270–300 | 840 | 500 |
| 1/2-20 | 480–690 | 290–410 | 1100 | 660 |
| 9/16-18 | 800–1000 | 480–600 | 1600 | 960 |
| 5/8-18 | 1100–1300 | 600–780 | 2400 | 1400 |
| 3/4-16 | 2300–2500 | 1300–1500 | 5000 | 3000 |
| 7/8-14 | 2500–3000 | 1500–1800 | 7000 | 4200 |
| 1-14 | 3700–5500 | 2200–3300* | 10,000 | 6000 |
| 1-1/8-12 | 5000–7000 | 3000–4200* | 15,000 | 9000 |
| 1-1/4-12 | 9000–11,000 | 5400–6600* | 25,000 | 15,000 |
* Estimated corresponding values (the AC's own footnote). The 7/16-20 row is printed as shown in the AC; its tension value (450–500) is a large step up from 3/8-24 (160–190), so check it against the manufacturer's data before relying on it.
Coarse thread series (in-lb)
| Thread size | Install: tension nut | Install: shear nut | Max: tension nut | Max: shear nut |
|---|---|---|---|---|
| 8-32 | 12–15 | 7–9 | 20 | 12 |
| 10-24 | 20–25 | 12–15 | 35 | 21 |
| 1/4-20 | 40–50 | 25–30 | 75 | 45 |
| 5/16-18 | 80–90 | 48–55 | 160 | 100 |
| 3/8-16 | 160–185 | 95–100 | 275 | 170 |
| 7/16-14 | 235–255 | 140–155 | 475 | 280 |
| 1/2-13 | 400–480 | 240–290 | 880 | 520 |
| 9/16-12 | 500–700 | 300–420 | 1100 | 650 |
| 5/8-11 | 700–900 | 420–540 | 1500 | 900 |
| 3/4-10 | 1150–1600 | 700–950 | 2500 | 1500 |
| 7/8-9 | 2200–3000 | 1300–1800 | 4600 | 2700 |
Same four columns and the same notes as the fine thread table.
How to read the four columns
All values are in inch-pounds (in-lb). The table has two pairs of columns, headed as in the AC:
Install = the AC's “torque limits recommended for installation (bolts loaded primarily in shear)”. Max = its “maximum allowable tightening torque limits”. In each pair the first column is for tension-type nuts (MS20365 and AN310; the AC's bolt stress basis is 40,000 psi for install and 90,000 psi for max) and the second for shear-type nuts (MS20364 and AN320; 24,000 psi and 54,000 psi).
AN310 is the castle nut and AN320 the castellated shear nut (par. 7-66 and 7-67). The castle nut is for bolts in tension; the shear nut is for hardware loaded in shear only.
Adding friction drag torque
Self-locking nuts and tight threads resist turning before the nut touches anything. That resistance is friction drag torque, and the table values do not include it. Par. 7-40c to 7-40g give the procedure:
1. Run the nut down to near contact with the washer or bearing surface and read the torque needed to keep it turning. That is the drag. 2. Add the drag to the torque you want. The sum is the “final torque” that should register on the indicator or be set on a click wrench. 3. Apply torque to the nut, not the bolt, whenever possible, with a smooth even pull.
Castle nuts: start the cotter-pin hole alignment at the minimum recommended torque plus drag, and do not go past the maximum plus drag. If the hole and slot do not line up, change the washer or the nut and try again (par. 7-40f). Bolt heads and cap screws: when torque goes on the head, apply the recommended torque plus drag (par. 7-40g).
Worked example — 1/4-28 castle nut
An AN310 castle nut on a 1/4-28 bolt, no manufacturer torque given. The drag torque measured with the nut run down is 10 in-lb. The 10 in-lb is an example value, not a table figure.
- Fine thread, tension-type nut, 1/4-28: install range 50–70 in-lb, max 100 in-lb.
- Final torque = table value + drag: 60–80 in-lb on the wrench.
- Start aligning the cotter-pin hole at 60 in-lb (minimum 50 + drag 10).
- If the slot is not lined up, you may tighten only as far as the maximum plus drag: 100 + 10 = 110 in-lb. Past that, change the washer or nut and try again (par. 7-40f). The AC says exceeding the maximum is not recommended.
Set 60–80 in-lb on the wrench, not 50–70. For feet: divide by 12 (60 in-lb = 5 ft-lb); for newton-metres multiply in-lb by 0.113.
Other points from par. 7-40 and 7-37
Bolt shank size, not wrench size. The thread size picks the row; the size of the socket or wrench is irrelevant. Clean and dry threads unless the manufacturer says otherwise. Calibrate the torque wrench at least once a year, or right after it is dropped or abused.
Smooth pull. If the wrench chatters or jerks during the final torque, back off the nut and torque again. Overtorque can fail a bolt or nut and many bolts need a stretch check before reuse. Thread showing. At least one thread of the bolt should stick out through a self-locking or plain nut.
Adapters. If an extension or crowfoot changes the effective length of the wrench, the wrench setting must be adjusted (par. 7-40h, Figure 7-2). The torque wrench extension calculator does that arithmetic.
Questions people actually ask
Do I torque the nut or the bolt?
The nut, whenever possible. That keeps the bolt from turning in the hole, which reduces wear (par. 7-40c). If the head must be turned, use the recommended torque plus drag.
What does drag torque mean for self-locking nuts?
Par. 7-40c asks you to check the torque needed to turn the nut once it is run down near the surface. Add that figure to the table torque. The table was derived without it.
Which column do I use for an AN310 castle nut?
AN310 is a tension-type nut, so use the tension column: install range for normal assembly, max as the limit. AN320 is the shear-type nut, which takes the shear column.
Why are two numbers given for installation but one for maximum?
The installation values are a recommended range. The maximum is a ceiling from the same table: the AC says exceeding it is not recommended.
Can I use these values on lubricated threads?
Not without data. The table is derived from oil-free cadmium-plated threads, and par. 7-40b says to keep threads clean and dry unless the manufacturer says otherwise.
Limits — when NOT to use this chart
Table 7-1 is a fallback for common cadmium-plated steel hardware, not the specification for a particular joint.
- The aircraft's manual governs. The AMM, SRM, engine manual or drawing torque overrides this table, including where it is lower.
- Cadmium plating, oil-free threads. The values come from that condition. Dry film lubricant, anti-seize, oil, stainless, titanium or aluminum threads change the friction. Use the manufacturer's value.
- Not every fastener is on the table. Hi-Lok, lockbolts, Cherry fasteners, studs, spark plugs, hose fittings, propeller and engine hardware have their own values.
- Close-tolerance and special bolts (AN173–AN186, NAS333–NAS340 and titanium NAS bolts) are interference fits. Do not substitute for them without the maker's or the FAA's instructions (par. 7-44).
- Torque does not replace locking. Safety wire, cotter pins and self-locking nuts keep the nut from turning. They do not hold torque (par. 7-122).
Sources
- FAA AC 43.13-1B CHG 1, Chapter 7, Table 7-1 (p. 7-9) — “Recommended torque values (inch-pounds)”: every number in the two tables, the caution, the footer and the asterisk note. Checked against the published page image.
- FAA AC 43.13-1B CHG 1, Chapter 7, par. 7-37, 7-40, 7-44, 7-66, 7-67 and Figure 7-2 — torque procedure and friction drag (7-40a to 7-40i), thread protrusion, castle and shear nuts, close-tolerance bolts, adapters.