It is a spring connecting the fork to the down tube. It adds a subtle self centering action to the front wheel, making loading and unloading of a bike with a basket, or say, Velo Orange's Porteur Rack much easier. The spring also offers some resistance to steering, so it counteracts deflections from hitting potholes and road debris.

• Mounts to the back of the fork crown via brake bolt or through bolt
• Fork crown mount diameter is made to fit an M6 bolt - common on nutted calipers
• Use Sheldon's Fender Nuts to work with recessed brake bolts
• Rust resistant and includes all required brackets and hardware
• Available for Small (31.8mm and smaller) and Large (38-62mm) sized downtubes
• Instructions can be found here