The Helios 44 58 mm F2 is one of the most mass produced lenses ever. Although the production has since stopped, there are still millions of them around making it a very affordable alternative. The Russian Hellios 44 is based on the lens formula of the Carl Zeiss Biotar 58 mm (I would not say it is a copy or clone of the Biotar, as the Helios looks and feels less well made and the pictures tend to be of lower quality). Although its naming might suggest otherwise, the Helios 44 is not a 44mm lens but a 58mm f2 lens.
It was manufactured with M42 mount, Pentax K mount and even M39 thread mount for the Zenit 3-M and the Revueflex M39 SLR cameras. Most lenses were manufactured in M42 to be used on Zenit Cameras. #Helios