Raise your hand if you’ve ever just grabbed a cable with a pliers and twisted them to tighten or stretch a cable. It may get the job done, but you probably kinked the hell out of the end of the cable. This cable stretcher by Park Tools is designed to properly stretch bike cables, but it should work on other equipment with similarly sized control cables.
Park Tool makes their cable stretcher from heat-treated steel, chrome-plates it, and adds cushion grips so it won’t chew up your hand.
You can operate the cable stretcher one-handed. You slip the cable into the jaws, put the moving arm of the jaw against a fixed object, and squeeze the handles to pull the cable tight. Park thoughtfully included a thumb lock to hold the cable stretched while you tighten the cable holder.
You can pick up a cable stretcher for $35 to $40.