Brake Pads - Yokozuna 54mm inserts, Salmon
If you're using Tektro R559 sidepull brake, the cartridge aluminum brake pad holders are already included with them so all you need to do to have new pads is slip these guys in.
These are about 54 mm long. Also available in a longer 73 mm length. Measure to make sure.
Sold per pair - as in one wheels worth.