From Amphenol's website:
Developed in the late 1940s as a miniature version of the Type C connector, BNC stands for Bayonet Neill Concelman and is named after Amphenol engineer Carl Concelman. The BNC product line is a miniature quick connect/disconnect RF connector. It features two bayonet lugs on the female connector; mating is achieved with only a quarter turn of the coupling nut. BNCs are ideally suited for cable termination for miniature to subminiature coaxial cable (RG-58, 59, to RG-179, RG-316, etc.)
Amphenol 50 Ω BNC connectors are miniature, lightweight units designed to operate up to 11 GHz and typically yield low reflection through 4 GHz. Designed to accommodate a large variety of RG and industry standard cables, BNC connectors are available in crimp/crimp, clamp/solder, SURETWIST®, and field serviceable termination styles. A full line of printed circuit board receptacles, bulkhead receptacles, resistor terminations, and other accessories complement the product offering.
A variety of our 50 Ω BNC connectors are recognized under the Component program of Underwriters Laboratories, Inc. These connectors are ideal for use with medical equipment and test instrumentation where safety cannot be compromised.
Amphenol also offers a full line of 75 Ω BNC connectors to meet the needs for higher performance impedance-matched cable interconnections. These connectors can be used in a variety of applications where true 75 Ω performance is needed to insure low signal distortion. Designed for the most popular 75 Ω cables used in broadcast and CATV applications as well as for plenum and other cables, these connectors feature crimp-crimp cable affixment for quick and reliable installation.
Two distinct types of 75 Ω BNC's are available, and both mate with each other and with 50 Ω BNC's. Type 1 is designated 75 Ω BNC-T1 and provides constant 75 Ω performance with low VSWR DC 4 GHz. Type 2 is designated 75 Ω BNC-T2 and is usable with low reflection DC - 1 GHz. For applications above 1 GHz, Type 1 is recommended.
Part numbers that are listed with the appropriate M39012 number are military grade connectors produced in accordance with and actively qualified to the military specification MIL-C-39012. Connectors not listed with the M39012 number constitute the industrial grade product offering. These connectors provide comparable performance and generally feature nickel-plated brass bodies, Teflon insulators, and either gold or silver-plated center contacts. Amphenols commercial grade connector offering carries the part number designation RFX for easy recognition. These low-cost connectors typically utilize die cast and molded components. While performance will not be equal to the industrial or military grade products, these connectors are ideal for use on a variety of commercial applications.
Reverse Polarity BNC's are also available. Reverse polarity is a keying system accomplished with a reverse interface, and ensures that reverse polarity interface connectors do not mate with standard interface connectors. Amphenol accomplishes this by inserting female contacts into plugs and male contacts into jacks. Other manufacturers may use reverse threading to accomplish reverse polarity keying.