Rings...

 From:  ed (EDDYF)
8907.11 In reply to 8907.10 
The 3D printing services will have Design Guides for each material offered. The guides show minimum wall thickness, minimum hole diameters, minimum clearance between two parts of a model, etc.

An example is here:

https://i.materialise.com/en/3d-printing-materials/design-guides

Ed Ferguson