Shimano SM-MA90 Disc Brake Adapter
Shimano's SM-MA90 series brackets are specifically designed for the new generation XTR-M985/988 disc brakes but can be used on all Shimano 74mm-caliper brakes.
Ok, it's a spacer. But Shimano stuff is always really nicely made, mounts up well, and best of all includes the necessary hardware. I've worked in auto repair for years and it's a nice bonus not having to hit the hardware store for every little project. Reasonably priced and way more sano than a goofy stack of washers!