Product Description: Full metal construction and aluminum anodizing process, durable for long-term use. Use this extension tube to get the correct image scale or the exact spacing required for reducers or field flatteners. The extension tube has a T2 internal thread and a T2 external thread to solve spacing problems in astrophotography and eliminates a range of focusing problems. The required spacing can be achieved by combining several extenders of different 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 Black color Please note: This Combi is M48 (48mm) thread caliber, not M42 thread caliber Due to different production batches, the two surface color paints (matte black; glossy black) are shipped randomly. Note: Please allow 0-2mm error due to manual measurement. Make sure you don't 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, please DO NOT order. Package includes: Optional 1 x Extension tube kit (size can be selected) Or 1 x Set of 8 M48 extension tube kits (3/5/7/10/12/15/20/30mm)