GR-900 series connectors were designed by the General Radio Corporation. The GR-900 adapters are a higher performance version of the GR-874 adapters. GR-900 adapters are a unisex connector type. Each connector is both female and male as they both have the same interlocking teeth and connection plates. GR-900 series connectors may have different locking collars. These represent different impedances: Stainless = 50 ohm, Black = 75 ohm.