Super -X- 40 IEC Metric Worm GearboxC input is hollow bore size in millimeters, after you select the ratio, input bore in mm i. e. C14 = 14mm, to make an XC close couple input gearbox you need to select and purchase a "C" motor adapter flange kit. "A" input is a solid shaft, to make an XF coupling style input gearbox you need to select and purchase an "F" Flange and coupling kit. NMRV Italian made drop in upgrade. Direct Interchange for Bonfiglioli W, Motovario NMRV, Ghirri MV, Varvel