Pin and Collar Fasteners: Hi-Lok, Lockbolts and Blind Bolts
Pin and collar fasteners are permanent two-piece fasteners for structural joints. Hi-Lok pins take a threaded collar whose wrenching section breaks off at a set preload, while lockbolt collars are swaged into grooves on the pin. Lockbolts are procured to NAS1413 with NAS1080 collars; Hi-Lok parts use the maker's HL numbers.
Updated
Pin and collar fastener types and where they are used
These fasteners replace a bolt and nut where the joint will not be taken apart in service and where weight, fatigue and installation speed matter. The FAA Airframe handbook (FAA-H-8083-31A, Chapter 4) describes the main families, summarized here.
| Type | How it locks | Notes from the FAA handbook |
|---|---|---|
| Hi-Lok pin and collar | Threaded collar with a wrenching section that shears off at a set torque | Pins in alloy steel, corrosion resistant steel or titanium; collars in aluminum, corrosion resistant steel or alloy steel |
| Hi-Tigue | As Hi-Lok, with a bead at the shank transition | Cold works the hole in a controlled interference fit for fatigue performance |
| Hi-Lite | As Hi-Lok, with a shorter transition and about one less thread | All titanium; lighter but lower clamp force; collars not interchangeable with Hi-Lok collars |
| Pull-type lockbolt | Collar swaged into annular grooves while a gun pulls the pintail, which then fractures | Used in primary and secondary structure, installed by one person |
| Stump-type lockbolt | Collar swaged by a riveting hammer and set with a bucking bar | Used where clearance will not take a pull gun; two-person install |
| Blind-type lockbolt and blind bolts | Installed from one side by pulling or by a drive nut | For joints with no back side access; each system has its own grip gauge |
| Eddie-Bolt 2 | Threaded collar deforms into five flutes on the pin | Clearance or interference holes; collar removable with special tooling |
The handbook lists typical lockbolt locations as wing splice fittings, landing gear fittings, fuel cell fittings, longerons, beams, skin splice plates and other major structural attachments. It also notes that lockbolts and Hi-Lok fasteners are often used for similar applications, and that blind bolts can sometimes directly replace either.
The specifications and part numbers that govern them
Lockbolts are covered by NAS standards. Hi-Lok, Hi-Tigue and Hi-Lite are proprietary systems from Hi-Shear, now part of LISI Aerospace, and are ordered by the maker's HL and related numbers, often called out directly on aircraft drawings.
| Spec or series | What it covers | Status or source |
|---|---|---|
| NAS1413 | Pull-type and stump-type swage locking pins and collars, flush or protruding head, for permanent structural attachment; procurement and quality conformance | 2016 revision listed as active; 2003 and 1997 revisions inactive (GlobalSpec) |
| NAS1080 | Lockbolt collars | Cited by Howmet as the collar standard |
| NAS7004 to NAS7012, NAS7014 to NAS7024 | A286 shear lockbolts, pull type, 100 degree intermediate flush and protruding heads | Howmet catalog, 1/8 to 3/8 in |
| NAS6974 to NAS6982, NAS6984 to NAS6992 | A286 shear lockbolts, stump type, 100 degree flush and protruding heads | Howmet catalog |
| NAS1465 to NAS1472 | Tension type, protruding head, pull type lockbolts | Howmet catalog cross-reference |
| NAS1414 to NAS1422, NAS1424 to NAS1432 | Lock bolts | Listed in AC 43.13-1B Table 7-12; check status before new design |
| NAS4006 | Aluminum coating for fasteners, including titanium pins | Active |
Howmet's A286 shear lockbolt page pairs the pins with NAS1080 collars in 2024-T4 aluminum, Monel or A286, and notes that some collar codes are double-ended collars for stump type only while others are beaded collars for pull type. The collar is not a generic item: it has to match the pin standard, the installation method and the material the drawing calls for.
Have a part like this?Send it in under a minute. A person replies within 1 business day.How the part number is built
Hi-Lok pin numbers follow a consistent pattern in published parts catalogs: series code, material and finish letters, then a diameter in thirty-seconds of an inch and a grip in sixteenths. Textron Aviation's parts catalog lists HL19PB5-7 this way:
- HL19: the series, a 100 degree flush shear head pin. The series number sets head style and pin design, not size.
- PB: the material and finish code. Distributor listings describe HL18PB pins as cadmium plated alloy steel; the HL10V pin in the same catalog is titanium.
- 5: diameter in thirty-seconds, so 5/32 in.
- -7: grip in sixteenths, so 7/16 in, listed as 0.4375 in.
The same rule fits the other catalog entries, for example HL19PB10-36 at 5/16 in diameter and 2.25 in grip. Collars follow the diameter rule: HL70-10 is listed as a 5/16 in aluminum collar with red anodize for shear applications, and HL79-10 as an aluminum collar with brown anodize and a threaded break-off style. Confirm every code against the current LISI Aerospace standard sheet before ordering, because the finish and lubricant letters vary by series and the FAA handbook warns that Hi-Lok and Hi-Tigue look alike and must be identified by part number, not by eye.
Interference fit, hole preparation and installation tooling
Hole size decides whether a pin fastener does its job. The FAA handbook says the Hi-Lok hole should be prepared so the maximum interference does not exceed 0.002 in, to avoid excess stress in the material around the hole, and that the hole edge is deburred so the head can seat over the radius under the pin head. It gives the usual practice as interference fit in aluminum structure and clearance fit in steel, titanium and composite structure. Hi-Tigue pins are the choice where a controlled interference fit is wanted, because the bead at the transition cold works the hole as the pin goes in.
Installation is different for each family:
- Hi-Lok: a hex key in the recess at the threaded end of the pin stops it turning while the driver runs the collar down. The wrenching section shears off when the design preload is reached, which the handbook says leaves the collar seated at the proper torque without additional torque inspection.
- Pull-type lockbolt: a pneumatic pull gun grips the pintail, draws the sheets together, swages the collar into the locking grooves and breaks the pintail off.
- Stump-type lockbolt: a riveting hammer with a swaging set and a bucking bar. Howmet notes that its stump type lockbolts are designed for automated installation equipment.
- Blind bolts: a pull tool or drive tool specific to the system. The handbook says every blind bolt system has its own grip gauge, not interchangeable with other systems, and that special removal kits exist for each type.
Tooling availability is a real sourcing constraint. Before choosing a fastener system for a new build, confirm the installer has the pull heads, swage sets, grip gauges and collar cutters for that exact system and size.
Inspecting installed fasteners
The FAA handbook gives a short acceptance check for lockbolts: the head must be firmly seated, the collar must be tight against the material with the proper shape and size, and pin protrusion must be within limits. The handbook prints a table of collar and protrusion dimensions by diameter; use the fastener manufacturer's current table or your process specification for acceptance values. For Hi-Lok joints, check that the wrenching section has broken off, the collar sits square against the structure and the pin head is seated, flush heads within the drawing's flushness limits.
Removal is part of inspection planning. Lockbolt collars are milled off with a collar cutter or split, with a backup block on the far side so the hole does not elongate, and the pin is driven out. Hi-Lok collars can be cut away the same way. A removed joint usually needs the hole checked and often an oversize pin, so record the hole condition on the nonconformance. Hole and fastener inspection methods are covered on the inspection and metrology page.
Materials, finishes and the trade-offs
Pins carry the load, collars hold the preload, and the pair has to suit the structure. The FAA handbook lists lockbolt pins in heat treated alloy steel or high strength aluminum alloy with aluminum or mild steel collars, and Howmet offers A286 pins with aluminum, Monel or A286 collars. Titanium pins are common in aluminum and composite structure for weight, and NAS4006 aluminum coating is used on titanium fasteners against galvanic corrosion. For blind bolts, the handbook quotes the Cherry Maxibolt at 112 ksi shear in steel and 95 ksi in A286, and the Huck blind bolt in A286 at 95 ksi shear.
Titanium, A286 and alloy steel pins are specialty metals under DFARS 252.225-7009 on DoD work, unless an exception such as the commercial fastener exception applies; see DFARS specialty metals. Alloy background is on the titanium alloys and stainless and specialty steels pages, and coating notes on surface finishing.
Ordering checklist
- Pin and collar part numbers as a matched set from the same system, with the standard or manufacturer sheet and revision. Do not mix Hi-Lok and Hi-Lite collars.
- Diameter, grip and any oversize, taken from a grip gauge or the drawing, not from an old parts list.
- Material, coating and lubricant codes, and a statement that alternates need written approval.
- Manufacturer and lot traceability for pins and collars separately, with a certificate of conformance and any NAS1413 quality conformance records the program requires.
- DFARS specialty metals flow down for titanium, A286 and steel pins on DoD work.
- Quantities with installation allowance, since collars and pins are single use once installed.
Counterfeit and quality risks, and how to receive them
Pin and collar fasteners fail quietly when the wrong collar, coating or oversize slips through. The risks are look-alike pins (Hi-Lok against Hi-Tigue, nominal against oversize), collars from another system that thread on but do not reach the design preload, missing coating or lubricant, and mixed lots. Receive them by checking full part numbers on each bag against the PO, measuring shank diameter and grip on a sample, confirming collar style and finish color against the standard, and matching manufacturer lot numbers to the CoC. Treat any surplus or broker source as high risk and apply the controls on the counterfeit parts avoidance page, with the receiving inspection guide for the dock.
How we source pins, collars and lockbolts
We do not stock fasteners or publish prices. We buy the exact pin and collar numbers from authorized and franchised distributors or the manufacturer, flow down the standard, coating and specialty metals requirements, and check the lot paperwork before shipment. They can go on one PO with the machined fittings or sheet metal they join, or be kitted by assembly. Discontinued numbers are searched under counterfeit avoidance controls; see obsolete aerospace parts. Threaded alternatives are on bolts and screws, nuts and washers, and the full range is on fasteners.
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Questions
How does a Hi-Lok collar know when to stop?
The collar has a wrenching section joined to the locking body at a designed fracture point. While a hex key holds the pin through its recess, the driver turns the collar until the clamp load in the joint reaches the design preload, at which point the wrenching section shears off. The FAA Airframe handbook notes that this leaves the collar seated at the proper torque without additional torque inspection, and the remaining collar cannot be overtightened.
Should Hi-Lok pins go in an interference fit or a clearance fit?
It depends on the structure and the drawing. The FAA Airframe handbook gives the usual practice as interference fit in aluminum and clearance fit in steel, titanium and composites, and says the hole should be prepared so interference does not exceed 0.002 in. Where a controlled interference fit is needed for fatigue, Hi-Tigue pins with a bead at the transition are used because they cold work the hole during installation.
What is the difference between pull-type and stump-type lockbolts?
A pull-type lockbolt has an extended pintail with pull grooves. A pull gun grips it, draws the joint together, swages the collar into the locking grooves and breaks the pintail off, so one person can install it. A stump-type lockbolt has no pintail; the collar is swaged with a riveting hammer and set while a bucking bar backs the head, so it is used where clearance will not take a pull gun.
Which standard covers lockbolts?
NAS1413 covers pull-type and stump-type swage locking pins and collars with flush or protruding heads for permanent structural attachment, including procurement and quality conformance. GlobalSpec lists the 2016 revision as active. Collars are covered by NAS1080, and individual pin series such as NAS7004 to NAS7012 for A286 pull-type shear lockbolts define the geometry. Name the revision your program accepts on the PO.
How do I tell shear lockbolts from tension lockbolts?
The FAA Airframe handbook says the easiest way is to count the locking grooves: tension pins normally have four locking grooves and shear pins have two. Do not rely on appearance alone for acceptance; confirm the part number on the drawing and the packaging, because pin series are easy to confuse.
How are installed lockbolts inspected?
The FAA Airframe handbook lists three checks: the head must be firmly seated, the collar must be tight against the material with the proper shape and size, and pin protrusion must be within limits. Acceptance dimensions come from the fastener manufacturer or your process specification. A lockbolt that fails is removed by milling or splitting the collar, with a backup block behind the work, and driving out the pin.
Related
Sources
- FAA-H-8083-31A, AMT Handbook Airframe Vol. 1 (2018), Chapter 4 special fasteners
- Howmet Aerospace: A286 CRES NAS shear type lockbolts
- Howmet Aerospace: alloy steel NAS tension type lockbolts
- GlobalSpec: NAS1413 lockbolt pins and collars, revision history
- Textron Aviation parts catalog: HL19PB5-7 pin listing
- Boeing Distribution: HL18PB6-2 Hi-Lok pin
- Military Fasteners: HL70-10 collar
- Military Fasteners: HL79-10 collar
- Boeing Distribution: NAS 4006 aluminum pigmented coating
- FAA AC 43.13-1B, Chapter 7: aircraft hardware, nuts, washers and tables 7-12 to 7-14
- DFARS 252.225-7009 (JAN 2023), specialty metals, COTS and commercial fastener exceptions
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