Adapter M54 external thread to M42 internal thread (M42 thread thickness is 2 mm) Type: monocular - Function: This adapter provides a secure bridge between M54 external threads and M42 internal threads in monocular setups. The M54 external side accepts a host with M54 threads, the M42 internal side accepts M42-threaded accessories. The M42 thread thickness is 2 mm. - Compatibility: Designed for monocular assemblies that use M54 external threads and for accessories with M42 internal threads, such as filters, tubes, and adapters. - Key specs: External thread: M54; Internal thread: M42; Internal thread thickness: 2 mm; Type: monocular. - Use scenarios: 1) Astronomy or wildlife viewing: connect a monocular to telescope or accessory components with M42 internal threads. 2) Photography: attach M42-threaded filters or extension tubes to a monocular that has an M54 threaded interface. 3) Field setups: quickly adapt between equipment with different thread standards in compact observing rigs. - How to use: Screw the M54 external-thread end into the matching M54-thread component. Then screw the M42 internal-thread side onto the M42-thread accessory until snug. Avoid overtightening.