Baader T-2 VariLock Extension Tube – 20-29 mmLockable T 2 extension tube, adjustable 20 29 mm with clamping Telescope side connection dimension: T 2 (M42 x 0. 75), Eyepiece connection dimension: Optional T 2 (M42 x 0. 75) or T 2 Ring Schwalbe 52 x 6. 5mm optical length: 20 29 mm continuously adjustable over millimeter scale Outer diameter: 50. 8mm 2 "inside diameter: with eyepiece side T 2 thread insert = 38mm with 52mm dovetail eyepiece sided = 42mm Both Baader VariLock T 2 (M42x0. 75mm)