As RonH. said, they are made by Sportworks, are very well made, easy to use, and do not damage your bike. The only warning is that they can (note: usually don't) damage fenders, since the retaining hook is designed to come down on a tire without fenders.
No fenders, no worries. If you want to use fenders (mudguards to Stepfam and probably Europa), then get the thick plastic or chrome steel type and stay away from aluminum (aluminium to Stepfam and probably Europa) and wooden fenders. Though . . . I have to say, the wooden ones are absolutely beautiful!
http://www.notempire.com/images/uplo...tled-1-823.jpg
Rick / OCRR