Aomekie Astronomical T2 Extension Ring Kit - Auto Focus Metal Maro Extension Tube adapter - Length 5mm 10mm 15mm 20mm - M48x0.75 on Both Sides - Accept 2inch Filters Male thread - M48*0.75, Female thread - M48*0.75 Length: 5mm 10mm 15mm 20mm Fully aluminium anodized black Use this extension tube for getting the correct image scale or the exact spacing required for reducers or field flatteners The required spacing can be achieved by combining several extenders of differing lengths,you can use 1 piece, 2 pieces , 3 pieces or 4 pieces of the extension rings as you like