What it is
Where to buyFAA-H-8083-31B (p. 4-55): tapered shank bolts such as the Taper-Lok are lightweight, high-strength shear or tension bolts with a tapered shank that gives an interference fit on installation. They can be identified by a round head (rather than a screwdriver slot or wrench flats) and a threaded shank. The Taper-Lok is a tapered conical-shank fastener installed into a precision tapered hole.
Use is limited to special applications such as the high-stress areas of fuel tanks. They look like Hi-Lok bolts after installation, but they have no hex recess at the threaded end. The collar has a captive washer and no extra washers are required.
The interference fit compresses the material around the hole, which gives excellent load transfer, fatigue resistance and sealing. Properly installed, the bolts become tightly wedged and do not turn while torque is applied to the nut.
Taper-Lok against Hi-Lok and sleeve bolt
| Feature | Taper-Lok | Hi-Lok | Sleeve bolt |
|---|---|---|---|
| Shank | Tapered, conical | Straight | Tapered bolt in an expandable sleeve |
| Hole | Precision tapered hole, reamed | Straight hole, clearance or interference | Standard-tolerance straight hole |
| Head of the threaded end | No hex recess | Hex recess | – |
| Washer | Captive on the collar | Separate when needed | – |
| Who installs | Trained personnel | Any qualified mechanic | Easier to install than the tapered bolt |
After FAA-H-8083-31B p. 4-55. For the sleeve bolt the handbook says the sleeve is internally tapered and externally straight, and that the bolt is forced into the sleeve, which expands and fills the hole.
The rule against substitution
The handbook states it twice (p. 4-55): it is important that a tapered bolt not be substituted for any other type of fastener in repairs, and equally important not to substitute any other type of fastener for a tapered bolt. New installation or rework of tapered shank bolt holes must be done by trained personnel.
A repair that meets a Taper-Lok hole therefore goes back to the SRM or the approved repair data; a straight-shank fastener in a tapered hole is not a repair.
Questions people actually ask
How do I tell a Taper-Lok from a Hi-Lok once installed?
They look alike, but the tapered shank bolt has no hex recess at the threaded end (FAA-H-8083-31B p. 4-55).
Can I put a Hi-Lok in a Taper-Lok hole?
No. The handbook says not to substitute any other type of fastener for a tapered bolt.
Why does the bolt not turn when I torque the nut?
Because the tapered shank wedges tightly in the tapered hole.
Limits of this guide
What the sources support, and no further.
- No hole sizes, taper, part numbers or grip data were found in a public text: the maker's data or the SRM is the source.
- No equivalents are given: the handbook forbids substitution.
- Tools and inspection of the tapered hole are not described in the sources used.
- 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 — P. 4-55: tapered shank bolts and sleeve bolts.