PrimaLuceLab T2 extensions are available in different lengths and they present on both sides of a T2 thread (one side is male, the other is female). Completely made of metal with black anodizing (both internal and external), these extensions offer external knurling for a better grip (very useful for example when screwing or unscrewing). Thanks to different T2 extensions and spacers, by ordering different combinations you can adjust the thickness of your personalized extension, in 0.5mm steps!
T2 extension rings have different use: can be screwed to optical accessories (such as field flatteners or focal reducers) to bring the camera sensor at the right distance from the lens (to optimize performance). They can be used to separate the mechanical accessories that, when used together, can touch and then not work properly (eg an off-axis guider could touch a filter wheel and it could prevent its rotation searching for a guide star)