The Dia-Compe AD-990 brake is one of the original U brakes in the market and still one of the best out there:

• Awesome stopping power makes this the brake of choice for riders that need a strong U-brake!
• Cold forged aluminum arms
• Dual spring tension adjustment
• Frame mounting bolts and brakes pads included
• Can be used for front or rear use. (This kit includes the FS-990 hardware so it can be used as a front brake as well. FS-990 sticker included)
• Center pull
• Weight: 300.5 grams / 10.6 ounces