Televue NP127is to OPTEC-3600 dovetail adapter. Fits 3.75"X24tpi male threads on OTA. 

Camera-side Compatibility:

• TCF-S3 series focuser,
• Pyxis 3" rotator,
• Perseus 4-port instrument selector,
• Any OPTEC-3600 receiver.

Specifications

• Overall Height: 0.96" (24.4mm)
• Clear Aperture: 3.15" (80.0mm)