$375 FIRM...this is a custom rear rotor size 10.5 made by lyndall racing for the rear brake setup on a 2014-15 sportster 48. Harley changed the rear rotor from 11.5 in 2014 and nobody has produced this size yet, it is a one of a kind. comes in black & chrome super lightweight. you can also get the matching 11.5 front rotor direct from lyndall. this rotor is brand new, never put on the bike. as far as I know, this is for a sportster 48 only, but i'm not a mechanic. this rotor, the "Gemini" series matches great with your stock spoke wheel. original cost $499

from lyndall:

When used with our Gold Plus, Z Plus and Xtreme Brake Pads, it provides the longest service life, and runs cleaner and quieter than any other braking system available for your motorcycle. The entire rotor weighs 1.6 pounds. Please see our application guide for fitments. Replacement parts are available for individual sale. A life-time warranty applies to the friction ring only if Lyndall Brakes are used on the rotor at all times.