The MIL-DTL-38999 specification describes several types of miniature, high density, bayonet and screw threaded circular connectors that use removable crimp or fixed solder contacts. Able to withstand harsh environments, these connectors are designed to operate across a temperature range of -65°C to +200°C. 

Built to the MIL-DTL-38999 standard (formerly MIL-C-38999) the connectors are used in the following types of application: Series I connectors are used where a quick disconnect coupling system is required for blind mating or other mating-difficult areas; Series II connectors are used where the connector is not subjected to high vibration or damp areas and where space or weight is at a premium due to their lower profile; Series III connectors are suitable for blind mating areas, and provide high-vibration characteristics at elevated temperature and are suitable for damp areas with the proper connector accessories; Series IV connectors are used where a quick disconnect coupling system is required for blind mating or other mating problem areas. 

Typical applications for MIL-DTL-38999 connectors and accessories include aerospace and military systems.