The Sennheiser MD 421 was released in 1960 to much acclaim, with a very tight cardioid polar pattern that borders on "supercardioid" at many frequencies and a clear, present sound that was far superior to most dynamic mics of the era.

The MD 421-U models (U-4 and U-5) feature a 3-pin XLR connector and a switchable high-pass filter that goes from "M" for music (full bandwidth) to "S" for speech (low frequencies attenuated). The U-4 model's original clip had a mount threaded for 3/8" stands, while the U-5 was threaded for 5/8" American stands. Being that most examples seen and sold today have replacement clips, this page will show both versions as they are otherwise interchangeable.