Halo Wheels 12 mm Thru x 142 mm Shimano/SRAM 8/9/10; Shimano Dynasys 11 Bicycle Rear Hubs
About Halo Wheels - "We didn't invent the wheel, we simply made it better."
This is hub spacing and is the width of the hub. It must match your frame specifications.
The cassette body type is the type of cassette and number of speeds the hub will accept.