Review on Female T2 M42 Step Up Coupling Adapter by Jay Huang

Many years ago some people made accessories for telescopes. Their factory was designed to produce tools with a thread pitch of 0.75mm. Instead of converting the standard 42mm x 1.0mm thread used for cameras, they made it with an odd 0.75mm pitch. So almost 100 years later we are suffering from two incompatible M42 streams. one is used on telescopes (42mm x 0.75mm) and the other on cameras (42mm x 1.0mm). When camera equipment needs to be connected to telescope equipment, an adapter ring is required. They were generally hard to find in a male versus female configuration at the time. I use it to mount a T2 eyepiece holder on the back of a Novoflex bellows with a Pentax M42 male thread mount. Usually I have to order them from China, UK or Russia and then wait a month for delivery. also pay double. At this price I'll grab a few more to keep on hand. I never know when I'll feel like trying an odd combination of devices. Note: https://www.amazon.com/dp/B07F868KSN is the opposite adapter ring. A matched pair is required to convert a T2 device to regular M42 streams. .Warning: Once one of these rings is screwed in place, it's likely that the ONLY way to remove it is "destructively" (see image).