Will this fit any internally geared bike?

It is made for bikes with an internal gear hub where the standard Thule hitch cannot clamp to the axle. Check your hub model and axle nut type against Thule's fit guidance before buying.

Do I need it for a derailleur bike?

No. Bikes with a standard rear derailleur and quick-release or thru-axle mount the Thule hitch directly. This adapter is only for internal hub setups.

Does it work with all Thule trailers?

It is designed to work with the Thule Bicycle Trailer Kit, the hitch system used across Thule's trailer range. Confirm your trailer uses that kit before ordering.

Will it stay on the bike permanently?

It mounts at the rear hub and can stay fitted between rides. It does add a step when you remove the rear wheel or service the hub.

Is it hard to install?

Installation is straightforward with basic tools and follows the included instructions. If your axle nuts or dropout shape differ from the spec, have a shop check the fit.