Optec DSI 35x24tpi Extension Tube, 1½” length

Optec-DSI 3.5-inch extension tubes feature female threads on one end with male threads on the opposite end with knurled bases to help attach and detach these tubes.  The extensions can be combined and stacked. Optec's four and five piece sets will provide all the needed extension for fixed focal length telescopes with 1/4" (6.35mm) increments using a minimum number of pieces.  Look at the "downloads" for a table of the optimized spacer combinations. 

All extensions and mounts are made from high strength 6061 aluminum alloy and black anodized.  Anti-reflection threading and internal baffles on the largest extension tube help minimize internal reflections.  All internal surfaces are painted and baked with a non-reflecting ultra-flat black paint.