Telescope T2-Extension Tube Kit for SLR Cameras and Eyepieces - Length 3mm 5mm 7mm 15mm 20mm 30mm 55mm - M42x0.75 on Both Sides (Upgraded)

Met my needs in connecting camera to telescope.

Dopo poche prove per capire gli anelli che dovevo utilizzare, la filettatura si è rovinata. Le 3 prolunghe più corte non si filettano più e ho rischiato di rovinare anche la camera alla quale li stavo collegando.

The thread on all of the larger rings are 4mm. In order for the 3mm to work correctly whatever you are screwing into the 3mm has to have 3mm or less thread length, otherwise it works the same as a 4mm ring. So if you need a 3mm ring measure the male thread of what you need it for. The other rings are fine and seem okay. I would not want to have to rely on un screwing these all of the time they do get stuck sometimes. I plan on using 422 thread lock and not unscrewing them....

Good range of sizes, I may buy another set. You can't have too many.

These work but the smaller sizes such as the 3, 5, and 7mm tubes are basically a one-and-done fitting because the threads will freeze up and be next to impossible to loosen. I sprayed the threads with silicone thinking that would help prevent them from locking up, but once I tightened them in my optical train I was unable to get them unlocked. I tried to carefully apply adjustable pliers to loosen but the aluminum material is so thin that they easily deform in the process of unlocking.