This flow cup, also called a viscosity cup, has a hole of 4 mm. It's a must-have for each ceramicist working with dipping glazes. The viscosity of a glaze is a very important variable to get good, consistent results. 
 
Dip the cup in the well mixed glaze. Measure the time it takes for the cup to fully empty. This run-through time (in seconds) gives an indication about the visocisity of the glaze. If the glaze is too thick (long run-through time) you can thin it with a deflocculant such as Dolapix. If it's too thin you can thicken it with a flocculant such as Epsom salts. 

The run-through time is indicated on the SOGO glazes.