This is one M42 mount lens rear cap. It is a compatible product. When a lens is attached to a camera body, caps must be stored separately. And they are easily forgotten and lost. Genuine caps are expensive, and it's a shock when you lose them. If you use this reasonably priced cap from the start, the shock will be less if you lose it. It is recommended to use this cap from the beginning, instead of using the genuine one regularly. Also, when you buy a used lens, caps may not be included. This cap can be used in such cases. Also, when using various mount adapters, Leica M mount is often used as an intermediary, but mount adapters often do not come with caps. Please use this cap as a substitute. Super-Takumar Super Takumar Takumar SMC Pentax Pentax Rear lens cap Rear cap