Flat surface, for flattening and a peen, for forging out.
30 cm. Relativly short handle, to provide better forging abilities (although opinions may vary, for me, longer handles are a torture)
Ergonomically shaped; Minimum difference in diameter over the total length of the handle, except the thickening at the bottom, to prevent the hammer slipping out of your hands. If you want to use a forging hammer the right way the handle should provide you good grip on every spot of the handle. Hard blows, hold the hammer at the bottom of the handle, soft blows, move your hand upwards the hammerhead. Therefor it’s important the diameter of the handle isn’t changing too much. It’s all about providing the same grip on every spot of the handle. Superficially burned for better grip. Waxed and treated with oil for longer lifespan. Secured with a wooden wedge plus a steel tunnel wedge.