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Threaded inserts (key-locked MS51830 / Keenserts, helical coil MS21209)

generic-NAS · Threaded insert · MS51830[-|CA|A][dash][L|LM] · e.g. MS51830CA106L (key-locked) · MS21209C0415 (helical coil, screw locking)

speclok.com
10/1/2026

Install sequence

1. Hole prepared
2. Insert in, keys driven

Traced from MS51835B (key-locked insert hole and assembly), p.1, 5, Figures 1 and 2. Not to scale.

Before you install

Sizes offered: Key-locked MS51830: internal .086-56 to .500-13 UNJC-3B and .190-32 to .500-20 UNJF-3B. Helical coil: lengths "1, 1-1/2, 2, 2-1/2 and 3 times the nominal thread diameter" (MIL-I-8846D §6.3.2)
Tool: Key-locked: standard drill, countersink and tap, then the Keensert installation tool drives the keys. Helical coil: STI tap, inserting tool, tang break-off tool
Special, non-proprietary tooling.
Training: PRC-9008 §9.0: "This process shall be performed by personnel qualified through training or experience and certified by their supervision to conduct the process." (NASA JSC process spec, helical coil)
Lead-time risk: Medium

Installed preload

Not applicable: inserts carry the screw's load into the parent material. MIL-I-45914A gives pullout and torque-out minimums (see datasheet strength); no preload is published.

Removal

Published: Howmet Keenserts Installation, Removal & Broach, Insert Removal (key-locked). Steps: speclok.com/tooling/threaded-insert#removal

Accept / reject after install

Key-locked hole: "Hole preparation in accordance with Tables I, II and III per applicable thread size of part and corresponding dash number." Example, MS51830-106 / -202 (.375-16): A .331-.336, CSINK B .385 (+.010 -.000), min full thread C .430 (MS51835B p.2, p.5).
Key-locked: "Install insert or stud as shown. (Keys locate correct depth.)" then "Drive keys as shown." (MS51835B Figure 2 requirements, p.5)
Helical coil, with countersunk hole: "The top edge of the insert shall be installed 0.75p to 1.5p below top surface of the tapped hole."; tang: "The tang should be removed from the insert after installation." (MS33537E sheet 2, 11.1 and 11.3)
Helical coil: "If the finished tapped hole gages satisfactorily, the installed insert will be within the thread tolerance when the insert meets the MS drawing requirements. It is, therefore, not necessary to gage the installed insert." (MS33537E sheet 2, 13)
Helical coil: "The minor diameter, countersink, and thread form of the holes shall be verified prior to installation of helical coil inserts. Post-process verification of insert depth and tang count (when tanged inserts are used) is required." (NASA PRC-9008 §8.0)

Check gauges

No insert gauge part number is named in the documents read; MS33537E checks the tapped hole, not the installed insert.

Sources: MS51835B · MS33537E · NASA PRC-9008 Rev E. Acceptance limits belong to the controlling spec: verify against your program's process documentation before use on hardware.

Sources

Before you install

Sizes offered: Key-locked MS51830: internal .086-56 to .500-13 UNJC-3B and .190-32 to .500-20 UNJF-3B. Helical coil: lengths "1, 1-1/2, 2, 2-1/2 and 3 times the nominal thread diameter" (MIL-I-8846D §6.3.2)

Tool: Key-locked: standard drill, countersink and tap, then the Keensert installation tool drives the keys. Helical coil: STI tap, inserting tool, tang break-off tool

Special, non-proprietary tooling.

Training: PRC-9008 §9.0: "This process shall be performed by personnel qualified through training or experience and certified by their supervision to conduct the process." (NASA JSC process spec, helical coil)

Lead-time risk: Medium

Accept / reject after install

Key-locked hole: "Hole preparation in accordance with Tables I, II and III per applicable thread size of part and corresponding dash number." Example, MS51830-106 / -202 (.375-16): A .331-.336, CSINK B .385 (+.010 -.000), min full thread C .430 (MS51835B p.2, p.5).

Key-locked: "Install insert or stud as shown. (Keys locate correct depth.)" then "Drive keys as shown." (MS51835B Figure 2 requirements, p.5)

Helical coil, with countersunk hole: "The top edge of the insert shall be installed 0.75p to 1.5p below top surface of the tapped hole."; tang: "The tang should be removed from the insert after installation." (MS33537E sheet 2, 11.1 and 11.3)

Helical coil: "If the finished tapped hole gages satisfactorily, the installed insert will be within the thread tolerance when the insert meets the MS drawing requirements. It is, therefore, not necessary to gage the installed insert." (MS33537E sheet 2, 13)

Helical coil: "The minor diameter, countersink, and thread form of the holes shall be verified prior to installation of helical coil inserts. Post-process verification of insert depth and tang count (when tanged inserts are used) is required." (NASA PRC-9008 §8.0)