Mayline or Alvin Parallel Bar Replacement Brake Knobs
$24.95
$33.95
Contains two front wire connectors, two rear pulley assemblies, and six 3/4" screws. Wire cable not included. Hardware kit for 36", 42", 48", 60" and 72" Professional Parallel Straightedge but can be used with most Universal Straightedges and Parallel Bars. This hardware kit assembles easily without complicated steps and is made from durable materials for long-term use.
Here are the instructions on How To Rewire a Parallel Bar