Strictly done, hammer levering would involve holding the sledge by the end of the handle, out at arms length, shoulder level. Using just wrist motion you lower the hammer back down to where it touches your nose. Most guys that lift could do a 8 lb. A twelve takes some grip stength. My goal is a 16.
Hammer work really works the wrists and overall grip. You can adjust the weight by simply sliding your hand closer to the head. Easiest way to get used to the motion and to get an idea of what you can do with one while trainig is start our with a broom. Wrsit circles, roling it different directions, etc. it will develop the wrist and forearm tremendously.
The thing with levering is the weight is part of the whole torque equation. While an 8 pound hammer sounds small, when you factor in the length of handle you're putting a lot more weight on your wrist.
I believe the equation is 8 lb x 36 inches length on the handle = 288 lbs torque on your wrist.
If anyone wants to correct my math, please do.