Product Fully metal construction and anodizing 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 Extension Tube Height: 3mm 5mm 7mm 10mm 12mm 15mm 20mm 30mm Male thread: M48*0.75mm Female thread: M48*0.75mm Color: Black Please Note: This Combi are M48 (48mm) thread caliber, not M42 thread caliber Due to different production batches, the two paint color on the surface(Matte black; shiny black) are shipped randomly. Note: Please allow 0-2mm error due to manual measurement. pls make sure you do not mind before you bid. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you If you really care about these details, pls DO NOT order. Package Include:Optional 1 x Extension Tube Kits(Size can be selected) Or 1 x set of 8 M48 Extension Tube Kits (3/5/7/10/12/15/20/30mm)