This SAE Aerospace Recommended Practice (ARP) defines the minimum across hexagon corner dimensions for fluid tube fittings and nuts. The ARP covers commonly specified inch and millimeter hexagon sizes.

The purpose of this ARP is to define the minimum allowable diameter of coners for hexagons that are machined from round stock or for hexagon corners that are turned to facilitate manufacutirng, installation, or other purpose. Rounded hex corners in accordance with this ARP shall not be used in conjunction with safety wire hoses per SAE AS 1043.