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Taper-Lok tapered-shank interference-fit bolts (NAS1724 / NAS1728)

PB Fasteners · Interference-fit tapered bolt · NAS1724 (100° flush) / NAS1725 (flush, O/S) / NAS1728 (protruding) / NAS1729 (protruding, O/S) · numbering not published free

speclok.com
10/1/2026

Install sequence

Installed

Installed view only (no public install sequence). Traced from NASA RP-1228 Fastener Design Manual, p.32, Taper-Lok; Figure 51. Not to scale.

Before you install

Sizes offered: Not published in the free documents (NAS1724 / NAS1728 are AIA standards)
Tool: Taper-Lok drill reamer and microstop drill cage for the tapered hole; nut torqued without holding the bolt
Proprietary system required.
Training: "New tapered shank bolt installation or rework of tapered shank bolt holes needs to be accomplished by trained personnel." (FAA-H-8083-31B p.4-55)
Lead-time risk: Medium

Installed preload

Not published in the free documents; nut torque values are not public.

Gauge kit (published part numbers)

Gauge	Sizes	Checks / limits	Source
TLG 5160	all	Taper-Lok fastener protrusion pin	AFFDL-TR-75-93 Interference-Fit-Fastener Investigation, p.47, Hole inspection
TLG 5120	all	Countersink depth gage	AFFDL-TR-75-93 Interference-Fit-Fastener Investigation, p.47, Hole inspection

Removal

No published removal procedure found; follow the manufacturer's instructions. Steps: speclok.com/tooling/taper-lok#removal

Accept / reject after install

"Properly installed, these bolts become tightly wedged and do not turn while torque is applied to the nut." (FAA-H-8083-31B p.4-55)
"The interference fit allows the nut (tension or shear nut) to be installed and torqued to the required value without holding the lockbolt to prevent rotation" (NASA RP-1228 p.32)
Interference from head protrusion: "Since the shank taper is 1/4 inch per foot, diametral interference is the protrusion difference divided by 48." (AFFDL-TR-75-93 p.90, a research report)

Check gauges

TLG 5160 fastener protrusion pin and TLG 5120 countersink depth gage, as used in AFFDL-TR-75-93 (p.47); no acceptance limits are published.

Sources: FAA-H-8083-31B p.4-55 · NASA RP-1228 · AFFDL-TR-75-93. Acceptance limits belong to the controlling spec: verify against your program's process documentation before use on hardware.

Sources

Before you install

Sizes offered: Not published in the free documents (NAS1724 / NAS1728 are AIA standards)

Tool: Taper-Lok drill reamer and microstop drill cage for the tapered hole; nut torqued without holding the bolt

Proprietary system required.

Training: "New tapered shank bolt installation or rework of tapered shank bolt holes needs to be accomplished by trained personnel." (FAA-H-8083-31B p.4-55)

Lead-time risk: Medium

Gauge

Sizes

Checks / limits

Source

TLG 5160

all

Taper-Lok fastener protrusion pin

AFFDL-TR-75-93 Interference-Fit-Fastener Investigation, p.47, Hole inspection

TLG 5120

all

Countersink depth gage

AFFDL-TR-75-93 Interference-Fit-Fastener Investigation, p.47, Hole inspection

Accept / reject after install

"Properly installed, these bolts become tightly wedged and do not turn while torque is applied to the nut." (FAA-H-8083-31B p.4-55)

"The interference fit allows the nut (tension or shear nut) to be installed and torqued to the required value without holding the lockbolt to prevent rotation" (NASA RP-1228 p.32)

Interference from head protrusion: "Since the shank taper is 1/4 inch per foot, diametral interference is the protrusion difference divided by 48." (AFFDL-TR-75-93 p.90, a research report)