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Hi Lock and Lock bolts

Hi Lock and Lock bolts

Hi Lock and Lock bolts


I have some questions about Hi lock and Lock bolt fasteners. I know a few things about them, both of them are composed by a pin and a collar, the Hi lock takes tension by the torque of the collar and the lock bolt takes the tension on the pin by the riveting machine, but ...

Which is the correct use for each of one in aa aircraft  structure? Which one is better than the other for different parameters, Fatigue, price,...

Thank you very much.

RE: Hi Lock and Lock bolts

Which is better depends entirely upon many perameters.
If your a bean counter, factors such as costs, availability, commonality are most important.
From a design view, it would be things like commonality, fit and function, physical constraints etc.
From a stress view it comes down to mechanical properties.
This is just a quick 30 second list which outlines some of the variables as to determine which is best.

As i have tried to get across, which is best depends upon what your trying to achieve and under which constraints.
Think about which is the best type of car, or colour, or even food.

RE: Hi Lock and Lock bolts

Tooling is the main difference in my mind.  With HiLoks all you need is a hex key and wrench (heck, even got those myself) but a Lock Bolt requires specific tooling to drive.  And tooling defines accessibility; none better than a HiLok for tight spaces.

Recollection is that hole tolerances are similar for both, so for the same diameter and material (and head style...) they can substitute for each other.  Done so many times, with the requisite analysis (for each case).

And what is the best kind of art or music.

RE: Hi Lock and Lock bolts

Both above are absolutely right. Hi-loks tend to be the most common because of their ease of installation. In general hi-loks are interchangeable with lock-bolts, both are pin fasteners. Lock-bolts have swaged on collars with large specialist tooling, hi-loks use threaded nuts that shear off at a pre-determined torque. Both fastener types are made in tension or shear types and use close tolerance reamed holes.

Our largest customer has a structural pin policy to replace with hi-loks whenever a lockbolt or hi-shear is removed for maintenance.

RE: Hi Lock and Lock bolts


Another "few points".

1. Cost/unit, swaged-collar [SC] lock-bolts will beat Hi-Loks. HOWEVER, tooling [costs, accessibility, etc] generally limits these to OEM [manufacturing] facilities.

2. For replacement purposes [repair], I favor pin/collar Hi-Loks. HLs resent many favorable options NOT available with SC lock-bolts: user-friendly installation (even in difficult areas); oversizes, head-styles, alloys etc (mix/match carefully); and availability.

3. NOTE [in general]:

3.1 SC lock-Bolts typically "max-out at 3/8" Dia [0.375"D] + 1-OS. Installation of larger collars is not practical due to increased "hammering" [setting] forces to deform the collars. Larger sizes generally means installation of bolts and nuts... or HL Pin/Collars.

3.2 Second oversize SC Lock-Bolts are "rare-to-non-existent".

3.3 Common Hi-Lok pin/collar sizes extend to +1.0"Dia in Nominal plus 1st & 2nd oversize... in most alloys. This allows HLs to replace heavier Bolt/Nut combinations [permanent installations]. Caution: up-to 1/2"Dia (+ oversizes) HLs pins/collar are fairly common/available. For 7/16" Dia [0.5625 D] and above, they become "special-order... with long lead-times.

3.4  WARNING. Shear-rated HL collars 1/2"-and-larger [0.500"D+] and tension-rated HL collars 7/16"D-and-larger [0.437"D+]  SHOULD NOT be installed by "hand". The collar-break torques are so high that most technicians will strain really hard to attain the torque; then loose control of the wrench/socket head when it suddenly breaks... which will fly around and damage structure [or hurt someone]. In these cases consider installation of a shear or tension rated nut at similar torque values [HL collar-break ranges].

3.5  Obviously, if a variety of diameters [small-to-large] are being installed, then it makes little sense to mix SC Lock-Bolts and HL Pins/collars: most OEMs will just install HLs to simplify logistics and assembly tooling. Exception: there are FOD critical high-vibration areas, such as engine-bays and inlets, where SC Lock-Bolts [or equiv] ... are mandatory.  or

3.6 There ARE OPTIONS to the SC Lock-Bolts and HLs, for smaller diameters, such as:
3.6.1 Two-piece "Eddy-Bolts" [hybrid lock-bolt with threaded/swaged collar].
3.6.2 One-piece "ductile-tail" shear-pins [IE: CherryBuck] [up to ~0.437Dia]
3.6.3 Blind-Bolts in close-reamed holes.

Regards, Wil Taylor

RE: Hi Lock and Lock bolts

One structural difference is that the collar of the Hi-Lok and Lockbolt are different.

The Lockbolt collar (tail side) can be installed on a taper.  Hi-Lok collars cannot be installed on a taper without a self aligning washer system or self aligning collar system.

However, Lockbolt collars can be installed on a tapered surface (up to 7 deg depending on the company and program model from what I've experienced).

A lockbolt collar can conform to a certain taper depending on the program and company and be totally acceptable.

When I am asked about substituting a Hi-Lok for a lockbolt the first thing I look at is if the tail side of the fastener structure has a taper.  Then I will compare the tention allowables for each.

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