Mech. The idler pulley and idler pulley were good quality and fitted perfectly, but the included strap was about Β½ inch too long for my application and was causing slippage. I checked the fit using Amazon's reference tool, so I'm not sure if it's an Amazon or Gates strap issue. Anyway, the belt is useless to me and since it comes with the kit it's all or nothing. Now that the idler pulley and idler pulley are installed I will consider this a lesson learned as I am not interested in returning all of the components in this kit to fix a belt issue.