MIL-F-18240 — Self-Locking Fastener Element (Legacy)
MIL-F-18240 originally defined the self-locking thread element used on externally threaded fasteners for service up to 250°F. Its final issue, Revision E (1 December 1989), was superseded on June 2, 1997 by MIL-DTL-18240F, which is the active governing document today.
At a Glance
Overview
MIL-F-18240 was the original specification covering self-locking elements incorporated into the threads of externally threaded fasteners — bolts and screws — used in applications where temperatures do not exceed 250°F, as a lock-wiring alternative. The specification went through several revisions between the early 1970s and 1989, when Revision E became the final "MIL-F" issue.
On June 2, 1997, the Department of Defense converted the specification to the "DTL" (detail specification) format as MIL-DTL-18240, Revision F, which superseded MIL-F-18240E and remains the active governing document. The technical scope — self-locking elements for UNC, UNJC, UNF, UNJF, UNRC, or UNRF threaded fasteners, in strip or patch configurations — carried forward essentially unchanged through the conversion.
- Some patent literature and older engineering documentation still references "MIL-F-18240" by name when describing the underlying locking-element technology, even though the governing document has since moved to MIL-DTL-18240.
Specification Lineage
| Document | Status |
|---|---|
| MIL-F-18240 (through Rev. E, 1989) | Superseded by MIL-DTL-18240 |
| MIL-DTL-18240F (1997–present) | Active, current governing document |
MIL-F-18240 is superseded. Current and future procurement should reference MIL-DTL-18240, which covers the same self-locking thread element under its current "DTL" designation. This page is retained for legacy drawing cross-reference only.
MIL-F-18240 — Frequently Asked Questions
Is MIL-F-18240 the same as MIL-DTL-18240?
They cover the same self-locking thread element technology. MIL-DTL-18240 is the current, active designation that superseded MIL-F-18240E in 1997 when the document was converted to the "DTL" specification format.
Why do patents and older documents still cite MIL-F-18240?
Documents written before 1997 — including some still-referenced patents on locking-element technology — predate the conversion to MIL-DTL-18240 and retain the original designation.
Need Self-Locking Fasteners to MIL-DTL-18240?
Ananka Fasteners supplies bolts and screws with current MIL-DTL-18240 self-locking elements, fully tested and certified.
Request a Quote