Void in the centre to accept 3 or 4 small coins - UK 5 pence - US Dimes.
 

Print 0.15 Solid infill

Print in half and place coins in and glue together. 

Gonggi is a Korean playground game that is traditionally played using five or more small grape-sized pebbles or plastic stones. It can be played alone or with friends. The stones are called gonggitdol (Korean: 공깃돌, lit. 'gonggi stones'). The game has five levels of increasing difficulty, testing hand-eye coordination, dexterity, and timing.