Common on European utility bikes, a front wheel stabiliser makes loading front racks simpler.
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 a VO Porteur rack much easier. You don't fight the bike while putting stuff in it, the front of the bike stays put. The spring offers some resistance to steering, so it counteracts deflections from hitting potholes and road debris too.
It's sized for bikes with a down tube of 1-1/4" (31.8mm) or smaller (get the large size for bikes with larger diameter down tubes). It connects to the fork via the brake pivot hole. The hole diameter is made for nutted calipers or a M6 bolt. For recessed mount calipers, minor modification with a drill or a file is necessary. You can also use Sheldon's Fender Nuts to allow the wheel stabilizer to be attached to a recessed fitting, if you don't want to drill or file it.
The wheel stabilizer is rust resistant, includes all the required brackets and hardware and has a pinch guard to cover the torsion spring. The little knob adjusts the spring tension.