Feed Through Termination, BNC Plug to Jack, (Conventional Male to Female), 1GHZ, 2W, 50ohm, F-BMBF0/1G2W50
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Part Number: F-BMBF0/1G2W50
Feed through terminations are used to match 50ohm or 75 ohm lines to the higher impedance inputs of, oscilloscopes and other electronic instruments.
The can be used either way around. They are essentially just 50ohm or 75 ohm resistors to ground but connected to both ports.