As a Kubota 121-3 excavator owner I thought I'd share this. It may or may not even pertain to your machine. On the Kubota kx121-3 which I think is basically a prior model KX 040 machine, it uses the 40 mm pin. That is the same pin diameter and ear spacing as the cat 303.5 and cat 304 machines. So you don't specifically have to limit yourself to a Kubota bucket. .