There are plenty of jokes about “hammer mechanics” that have more than a grain of truth, but every good mechanic needs at least a small quiver of hammers to work efficiently. You will want a hammer with some sort of soft face for common work. These can be rubber, rawhide, lead, brass, aluminum or dead-blow. Lead hammers are pretty specialized, so a common rubber or dead-blow hammer will be the most useful for general work on a bike. Rubber doesn’t mar hard surfaces, but the head is large and difficult to aim in tight spots. Plus, the rubber hammer will rebound off the surface you strike. A dead-blow hammer (shown) is generally made of a resilient plastic with a hollow head filled with sand or lead shot. The plastic isn’t quite as benign as rubber, but still won’t damage most surfaces. The dead-blow hammer has some weight to it in a smaller head that is easier to aim than rubber. The dead-blow concentrates the force well, and doesn’t rebound. For some heavy work like driving in bearings or knocking out races with a punch, you need a steel hammer. Not a carpenter’s claw hammer, but a Ball Peen hammer made to strike steel. For a long time I didn’t see the need for a quality, brand-name hammer, but after getting one I was amazed at the difference. Mine has a precision-ground face and a shock-absorbing handle. I can’t stand the feel of a cheap hammer anymore!