Complex sentence: They were usually supplied with Zenit cameras and thus usable with other M42 lens mount cameras such as the Pentax Spotmatic.Some later Helios models were built also for the Pentax K mount.
Split into simpler sentences: They were usually supplied with Zenit cameras and thus usable with other M42 lens mount cameras such as the Pentax Spotmatic. Later Helios models were built also for the Pentax K mount.