If you have a broken bolt that needs to be glued, the best thing to use is a strong adhesive. There are many adhesives on the market that will work for this purpose, but you want to make sure you get one that is specifically made for bonding metal. Once you have your adhesive, simply apply it to both surfaces of the broken bolt and press them together. Hold it in place for a few minutes until the glue sets, then let it dry completely before using the repaired bolt.