Least Material Condition
Of particular note in the MS21042 series of nuts is the nuts wall thickness. The drawings below illustrate the wall thickness of the MS21042 series as compared to nuts of similar sizes, such as the 42FLW lock-nut series, MS21043 series, and MS21044N series of lock-nuts.
Below are downloadable PDFs of all of the LMC drawings above:
MS21042 Series | Cadmium Plated Steel-Alloy Lock-Nut
MS21042L Series | 'L' - Dry Film Lubricated
MS21043 Series | Dimensionally the same as MS21042, only made of stainless
MS21044N Series | A hexagonal self-locking nut with nylon insert
NAS1804 Series | 12 point lock-nut, which is dimensionally similar to the MS21042 series. Made of alloy steel and cadmium plated
NAS1805 Series | Dimensionally the same as the NAS1804, only made of A286. May be cadmium or silver plated, and with or without lubricant.
The NAS1291 series are dimensionally the same as the MS21042 series, with the addition of larger thread diameters up to .6250" . NAS1291-02 thru -6 are inactive for design, and have been superseded by NASM21042. NAS1291C04 thru C6 were superseded by NASM21043:
NAS1291X | Cadmium Plated without Lubricant
NAS1291 | Cadmium Plated, Dry File Lubricated
NAS1291C | Stainless A286, Silver Plated, without Lubricant