The ring has an inner diameter of 19mm. You can adjust the size by scaling in the slicer or you can adjust all dimensions via changing the variables directly in Onshape: 

If you want to add your own signet you can perform a substraction in the slicer or you adjust the sketch "signet-drawing" in Onshape.

Printing suggestions:

• Put the flat signet face on the bed.

• Use concentric bottom surface pattern.

• You can use a different color for the first 2-3 layers.