Replacement coupler for Trail-Gear dual case adapters. Use this coupler to upgrade your rear input from 21 to 23 or to replace a worn coupler. Available in 21 or 23 spline (please count the input splines on your rear case input shaft!). Fitment is only guaranteed on Trail-Gear dual case adapters. 26 spline fits 2.7 manual transmission style adapters ONLY!