Circular Connectors requiring a backshell adaptor are generally MIL-Spec (military specification) connectors.MIL- Spec circular connectors are primarily used in Aerospace, Military and rugged Industrial applications. Their circular design enables quick and easy connection, with accessory threads for a range of backshell adaptors. The most common series of MIL Circular connector types are the MIL-DTL-26482 Series I and II, and the
MIL-DTL-38999 Series I, II, III and IV.