I used a 3/4" copper sweat coupling, turned a tenon for a tight fit on the end, put the fitting on before inserting the tool into the hole. Rather than hammer on the tool, I started the tang into the hole then tapped the but end of the handle with my dead blow mallet. this will cause the tool to gently creep back into the handle until it is fully seated without doing any damage to the tool. If the tenon gets a bit too small, you can always drill a small hole through the copper and pin it with a small nail.
Charles