If you've ever used a hacksaw or reciprocating saw to shorten a machine screw, carriage bolt. or threaded rod, you've probably discovered the nut won't go back on after you saw through the metal fastener. That's because the saw has deformed the threads and created prickly burrs. The next time you need to shorten a screw, bolt or rod, try this: Put the nut onto the threaded end of the fastener before making the cut. Once you have sawed through, back off the nut using a wrench. The nut will re-form the threads and shear off any burrs.