Martinez M4W 12OZ Wide Claw Smooth Face Replacement Head for the M4 Titanium Hammer – Also Fits M1 Hammer
Some of the smooth faces have been powder coated black. You may find that the powder coat will chip. This will not affect the performance of the hammer in anyway, however, if you are concerned about it, you can safely sand off the powder coat with a sander to reveal the smooth steel face.
Spanner to change head is available here