This hammer/mallet head allows for a heavier material to be inserted into the cutouts and sealed in to save filament while still providing a good heft. I glued my caps on with E6000. The design calls for a 3/4in PVC pide of any lenth to be press fit into the center hole to act as a handle. You may glue the head on or simply use the press fit for a more portable mallet.
I printed mine with a 0.6mm nozzle with 0.3mm, 5 walls, 6 top and bottom layers, 80% cubic subdivision infill. Then filled it with metal BB's with a resulting weight of about 200 grams.
Print the plugs at 96% size for a more flush fit, at 100% they protrude a bit