U This is a security reference. He is well known among fixies lovers in particular. It is very short (14cm to 8.3cm wide), allowing to interfere attacks lever. It is very robust and well finished. Although it is not indicated, it comes with a media type EZ mount (very convenient, the U does not move once fixed). Another nice point, it comes with three keys, one with a small integrated LED lamp. Convenient to find the lock when it is dark!