This is the V2 pulley for your Autotrickler. The only reason you would need to buy this is if you had a V1 and upgraded to V2 (or if you somehow damaged your pulley). The V1>V2 upgrade did not come with the V2 pulley, and the V1 pulley does not fit in our base with the larger belts now provided by Adam. We will also include one of the larger belts.
If we just confused the hell out of you with that paragraph, give us a call if you have any questions.