If you're looking to adapt your Mercury wheels to handle a different make/model of cassette cogs - this is the right spot. You're also in the right spot if you've put some miles on your wheels and you're ready to grab a fresh freehub of the same type.
To order a replacement, you'll need to know a little about the drivetrain on your bicycle and the specific hub used on your wheel.
The Hub Model # must match your hubs or the freehub body will not fit correctly.
If you'd like some help determining the right freehub, email a picture of the hub shell to firstname.lastname@example.org.