Gearbox Round Nut M20*1.5 (3 Pieces) For 105-135 Gear Box of 4 Stroke (178F, 186F, 188F & 177F) Power Tiller is a precision-threaded round nut set, designed for secure fastening and alignment inside the gearbox assemblies of 4-stroke power tillers (compatible with engine models 178F, 186F, 188F, 177F). Manufactured to M20 x 1.5 metric fine thread standards, these nuts ensure reliable locking and stability for critical gearbox components during heavy-duty field operations.