With the exception of aircraft-grade NAS hardware, Grade-8 bolts are the strongest bolts available. They are identified by five raised lines stamped onto the head of the bolt in a star pattern. Grade-8 bolts are used in applications where high tensile strength is required. Sometimes it is necessary to shorten the bolt. Grade-8 bolts are difficult to cut, but can be done with the use of a high-speed cutoff wheel.
Clamp the bolt by the head into a bench vice. Aluminum soft-jaws or wood inserts will prevent marring of the bolt head.
Put your safety glasses on and install the diamond cut-off wheel to the Dremel tool.
Mark the bolt where you want to cut it and run a nut onto the threads of the bolt, past where you will cut. Make sure the nut will not get hit by the cut-off wheel.
Turn on the Dremel and cut the bolt at the spot you marked. The cut-off wheel works best the faster it is spinning. Do not allow the tool to bog down.
File off any burrs and sharp edges off the end of the cut bolt. Run the nut back off the threads. The nut will straighten any threads that may have been damaged or bent during the cutting process.
A high-speed pneumatic cut-off wheel can also be used instead of a Dremel. The discs for the pneumatic tools are much thicker and will remove more material, so mark your line appropriately.
Wait until the bolt cools down before you pick it up. It will be very hot from the cutting and may burn your fingers.