Gsoky Astronomical T-Thread Spacer Ring / T2 Thread Extension Tube - T-Mount Extension Ring - Length 30mm - M42x0.75 on Both Sides Male thread - M42*0.75 Female thread - M42*0.75. Idea to link or extend 30mm of the M42*0.75products Length 30mm and external diameter of the tube is 44mm . Fully aluminium anodized black.