Tektro Seat Post Clamp w/ Rear Cable Hanger 32.0
Tektro 1276A Seat Post Clamp with Rear Cable Hanger 32.0 mm
My favourite style of brake is the cantilever. I much prefer them over less expensive linear pull V-brakes. However if you want to make the swap (and from calliper brakes too,) you'll need cable hangers. These little devices provide a spot for the cable housing to stop securely and allow the cable to travel to the centre line of the transverse cable connecting the two sides. You can't have cantilevers without them.