1955-79 bus torsion spring narrowing jig. This kit makes it very simple to narrow your own bus spring packs, saving you money. This kit comes with the drill jig and a 3/8 x 90-degree spotting drill bit. Instructions can be found here. Tools needed to do the job. 3/8 hand drill or drill press Angle grinder/Sander Cut of wheel Hammer Allen wrench.