I know you all have probably switched completely to metric, but as a Canadian we have the strange hybrid being so close ot the USA.
A teaspoon is not just a metal thing that you stir tea with, it's an actual unit of measure, and the measuring spoons that we can get in 1/2 and 1/4 teaspoon is a specific volume measured level on the spoon. I'm sure that you have measuring spoons that do ml that are similar for cooking