QUICK AND EASY MOWER SPINDLE TEST Model Z 400 Z 500 Grand Stand Zero Turn Rider. Toro 107-8504 Zero Turn Mower Spindle Assembly Z Master Z400 Z500 GrandStand 3PkThis spindle assembly will replace the following Toro Models. 21×11-10.21×1100-8.224×1200-12.225×1100-10.22×1000-14.22×11-10.22×1100-10.22×950-10.23hp.