A “-4” tube sleeve is a sleeve for an AN (Army-Navy) 37-degree flared fitting, designed to be used with a number 4 tube nut. The “-4” refers to the dash size, which indicates the tube’s outer diameter (OD) in sixteenths of an inch. A dash 4 (-4) sleeve is used for 1/4-inch OD tubing.

These sleeves are primarily used in high-performance hydraulic and aerospace applications.