Types, pins and collars
Where to buyFAA-H-8083-31B (pp. 4-50 to 4-52): three types are in common use. The pull-type is the most common in primary and secondary structure, is installed very rapidly by one operator with a special pneumatic pull gun, and weighs about half of the equivalent AN steel bolt and nut. The stump-type has no pull stem and is used where clearance does not permit the pull-type; it is driven with a pneumatic riveting hammer with a set that swages the collar, and a bucking bar. The blind-type is a complete unit used where only one side is accessible.
Pins of pull and stump types are heat-treated alloy steel or high-strength aluminium alloy; collars are aluminium alloy or mild steel. The blind type has a heat-treated alloy steel pin, a blind sleeve, a filler sleeve, a mild steel collar and a carbon steel washer. Tension pins normally have four locking grooves and shear pins two; the tooling preloads the pin while swaging and the surplus end of the pin, the pintail, breaks off.
Howmet lists NAS lockbolts produced to procurement specifications NAS621 and NAS1413, in titanium, alloy steel, A286 CRES and aluminium alloy, and its own GP, LGP, XPL, HuckComp and LHP families.
The hole
Hole preparation for a lockbolt is similar to that for a Hi-Lok: an interference fit is typically used for aluminium and a clearance fit for steel, titanium and composite (FAA-H-8083-31B p. 4-52). The maker's hole limits for each pin size are in its catalogue; the only public figures found are those of the table below.
See the Hi-Lok holes and drills guide for the pilot and final drills of the Hi-Lok that lockbolt holes follow.
Huck lockbolt, Hi-Lok and NAS numbers, with the hole
| Huck | Hi-Lok | NAS | Hole, in | Drill inside |
|---|---|---|---|---|
| R 3001-5 | HL18-5 | NAS1465 | 0.161–0.164 | #20 (0.1610) |
| R 3001-6 | HL18-6 | NAS1466 | 0.185–0.188 | 12/64 (0.1875) |
| R 3001-8 | HL18-8 | NAS1468 | 0.242–0.246 | C (0.2420) |
| R 3001-10 | HL18-10 | NAS1470 | 0.307–0.310 | no standard drill inside: ream |
| R 3002-5 | HL21-5 | none printed | 0.161–0.164 | #20 (0.1610) |
| R 3002-6 | HL21-6 | NAS1956 (as printed) | 0.185–0.188 | 12/64 (0.1875) |
| R 3002-8 | HL21-8 | NAS1458 | 0.242–0.246 | C (0.2420) |
| R 3002-10 | HL21-10 | NAS1460 | 0.307–0.310 | no standard drill inside: ream |
TM 1-1500-204-23-6 Table 2-6, Huck and Hi-Lok Bolt Substitution (p. 2-24). The table prints the three numbers in the same row against one hole diameter range; the drill column is our pick of the drill that falls inside the range, and “ream” where none does. The manual allows standard bolts in place of Huck bolts only when Huck bolts or equivalents are not available, in a hole that gives interference fit with the shank.
Inspecting and removing
| Item | What | Source |
|---|---|---|
| Head | Firmly seated | FAA-H-8083-31B p. 4-52 |
| Collar | Tight against the material, with the proper shape and size (acceptance dimensions in the maker’s figure) | p. 4-52, fig. 4-108 |
| Pin | Protrusion within limits | p. 4-52 |
| Removal | The best way is to remove the collar; a collar cutter on a drill motor mills it off without damaging the skin, and a backup block on the far side prevents hole elongation if a splitter or chisel is used | pp. 4-52, 4-53 |
Every make has its own grip gauge and installation tool (FAA-H-8083-31B p. 4-50). Lockbolts are a permanent fastener; MIL-HDBK-5J lists them with the “Hi-Shear” rivets and Cherrybucks as swaged collar fasteners.
Questions people actually ask
How do I tell a tension pin from a shear pin?
Tension pins normally have four locking grooves and shear pins two (FAA-H-8083-31B p. 4-52).
Pull-type or stump-type?
The pull-type when the pull gun fits and one operator is available; the stump-type where clearance does not allow the pull gun.
Can a lockbolt be reused?
No. The collar is swaged on and is cut off to remove the fastener.
Limits of this guide
What the sources support, and no further.
- No hole table by diameter for aerospace lockbolts is public in the sources used; the only figures are the Huck rows of the Army manual.
- Strength and part number letters of the NAS and maker families are not given.
- Pin and collar numbers (for example the collar for each pin) are not given: use the maker's catalogue.
- Reference data, not approved data. The SRM, the drawing or the approved repair data governs over every figure here.
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Sources
- FAA-H-8083-31B, Aviation Maintenance Technician Handbook, Airframe, chapter 4 — Pp. 4-50 to 4-53: lockbolt types, pins and collars, hole fit, inspection, removal.
- TM 1-1500-204-23-6 (with Change 4) — Table 2-6, Huck and Hi-Lok Bolt Substitution, p. 2-24.
- Howmet lockbolts — NAS lockbolts to NAS621 and NAS1413; GP, LGP, XPL, HuckComp and LHP families.
- MIL-HDBK-5J (31 Jan 2003), section 8 — Swaged collar fasteners and blind fasteners, definitions.