Improved version of a printable Tromner style neurological reflex hammer. This one is slightly larger and better balanced; has a cavity in the body for adding additional weight to improve the balance further, and makes it quite usable.

No

0.2 mm

Any

Print the head and the cap standing up with the front face on the build plate.
Use at least 3 perimeters for strength. The "skeletonized" handle look in the picture is created by using 6 perimeters, no infill and no top/bottom layers.
If you intend to actually use it as a reflex hammer, the bumper part should be printed hollow using a flexible filament. Alternatively mold part can be printed (x2) and used to form the bumper part out of moldable silicone/rubber material (such as casting silicone or Sugru).

The hollow portion of the hammer head can be filled with a heavy material such as small lead fishing weights, ball bearings, or even just clay. I used hot glue to pot it in to reduce rattling.