Will this fit my rear rack?

If your rack width falls between 60–80cm, the adapter will clamp down. Measure your rack width at the top where the tubes sit — if you're outside that range, this won't work.

What hardware do I need to install it?

The adapter ships as-is. You'll need bolts or clamps to secure it to your existing rear rack — those aren't included, so check what your rack uses before ordering.

Can I use this for tubes only, or other cargo too?

It's designed as a tube holder, but you can strap other lightweight cargo to it. Don't exceed what your rear rack is rated for — the adapter just holds it in place.