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.
The Shimano SM-MA90 Disc Brake Adapter is available in five versions to fit 160mm and 180mm rotors for front IS Mount or front Post Mount (also referred to as PS or Post Standard) as well as rear IS Mount
IS: 51mm International Standard, PM: 74mm Post Mount
Showing Questions 1 of 1
Q: Which one of these adapters do I need to mount an IS caliper to a Post mount frame with a 180mm rotor?
A: Unfortunately, we do not currently have a bracket for mounting 180mm rear post mounts.
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!