Avid Disc Brake Adaptors.
You need to know three things -- what kind of mount your Shimano disc caliper is, International Standard (ISO) or post mount. If it goes on the front, you need to know what your fork is: ISO, post-mount, or a few special cases (Marzocchi 20mm axle, Boxxer
For 74mm caliper on 74mm fork, using 203mm rotor
Includes mounting hardware