http://www.woodcarvingguru.com/fiberglass-handle/
How to fix a hammer….?
I have a fiberglass hammer with a rubber slip-on handle “cover.” It is slipping off. 
Suggestions on how to “glue” it back on, including what type of glue certainly would be appreciated.
Lawrence
http://www.truebiblesermons.com
That “handle cover” is called the grip.
Rubber (probably neoprene in this case), being a pliable substance, tends to resist being glued.
Suggest completely slipping the handle grip off of the handle, clean & dry the handle with rubbing alcohol, clean (as best you can) & dry (must be dry!) the inside of the grip, put a coat of rubber cement on the lower half of the handle, and then slip the grip back on. The act of slipping the grip back on will spread the rubber cement. Let the rubber cement cure for at least 24 hours. Rubber cement smells to high heaven, so you probably want to leave it out on the back porch…