(AKA K-Nuts or Kaynuts) These are reduced hex and reduced height, all-metal self locking nuts. Jet nuts are lightweight and made of corrosion resistant steel with high strength (160,000 psi tensile) and heat resistant (to 450F).
Naming convention: MS21042-(size)
SizeThreadHex Size (in) OD (in) Max height (in)
04
4-40
5/32