Mazda MX-5, Miata, Eunos Mk4 ND (2015-) Rear Diff Mount Insert - PFR36-630BLK These inserts are designed to fill the voids in the original bush, providing a quick and easy way of limiting the differential movement and resulting in greater stability under acceleration. Fits manual transmission only. - NOTE: Price is for CAR KIT, NOT per bush… Powerflex price their bushes individually, but we have combined the quantities to make it simple!