Hourglass desk toy

Fusion 360 design of hourglass. It has 2mm wall. 

“Sand” fill

I used ca. 0.8mm steel balls that I use when I want to make my prints heavier. 

For more ordinary “infill” sand is possible but it needs to be very dry and never get damp. 

I'd opt for something like millet or silica gel balls or some “round grocery”. 

Testing orifice size

It's hard to estimate what hole size is needed. For me it was about 4x of particles size, but it depends on the weight and shape. 

Take a piece of paper and glue/tape it to a roll. Then cut off the tip piece by piece until you get a steady flow through a hole. Then measure the hole and download respective model. Or adjust the Fusion 360 parameter and make your own.