I made these coasters in 2 parts that click together.
There is a groove in the bottom of the coasters so they stack nicely on top of each other.
The diameter of these coasters is 90mm.
The height of the coasters is 4mm (this is including the height of the black edge that is used to stack the coasters which is heigher than the rest of the coaster)

The black part took 1hour to print and the yellow part took 20minutes to print.

I have also made the same kind of coasters but with the radiation sign!!
The stackable radiation coasters are compatible with these biohazard coasters.
https://www.thingiverse.com/thing:3051476