35.3mm T-to-T spacer (M42 female to M42 male).  This adapter takes up 35.3mm of the Starizona SCT Corrector's 90.3mm back focus. Leaving 55mm of backfocus to work with. Ideal for common setups such as DSLRs with T-rings, or ZWO cooled cameras and their 16.5mm and 21mm stock adapters.