Fully metal construction and aluminum process, durable for long time use. Use this extension tube for getting the correct 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 Tube SIZE: M42 x 0.75 Type: Monocular Extension Tube Height: 3mm 5mm 7mm 10mm 12mm 15mm 20mm 30mm Why use its When you cannot get 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 various adapters. The M42 x 0.75 threads on both ends make it extremely versatile. Use this extender for obtaining the correct 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:black Material:aluminum Package Contents: 16 x M42 x 0.75 Thread Extension Tube(3/5/7/10/12/15/20/30mm) Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.