Fully metal construction and aluminum process, durable for long time use.Use this extension tube for the image scale or the exact spacing required for reducers or field flatteners.The extension tube has a T2 interior thread and a T2 exterior thread for solving spacing problems in astrophotography and eliminates a range of focusing problems.The required spacing can be achieved by combining several extenders of differing lengths.Type: Astronomical Telescope T2 thread Extension TubeSIZE: M42 x 0.75Type: MonocularExtension Tube Height: 3mm 5mm 7mm 10mm 12mm 15mm 20mm 30mmWhy use ?When you cannot to the right plane for focusing with a camera or eyepiece. This extension tube kit solves this problem. You can use this extender with any camera or eyepiece or with adapters. The M42 x 0.75 threads on both ends extremely versatile.Use this extender for obtaining the image scale or for the exact spacing required for a reducer or field flattener. You can reach the extension length required by combining several extenders of different lengths.colour:blackMaterial:aluminumPackage Contents:8 x M42 x 0.75 Thread Extension Tube(3/5/7/10/12/15/20/30mm)