You must be logged in and verified to contact the designer.
Product Description
Inside diameter modelled at 20.55 which should print to 19.55mm or *very* slightly larger.
See my other GL rings in different sizes:
https://www.shapeways.com/model/331435/green_lantern_ring_9_5.html?gid=ug
https://www.shapeways.com/model/318330/green_lantern_ring_16_8mm.html?gid=ug
https://www.shapeways.com/model/310333/green_lantern_ring_size_12.html?gid=ug