Bargain Shimano Center-Lock Disc QR x 135 mm Bicycle Rear Hubs
About Shimano - "Shimano practices good local citizenship, pursues continued access to those areas that are enjoyed by outdoor enthusiasts, and is committed to minimizing our impact on the environment."
This should correspond to the type of brakes you have on the bike.
This is hub spacing and is the width of the hub. It must match your frame specifications.