I designed this drain fitting for a coworker whose home was built in the 1970s with a plastic shower drain fitting that had become cracked.

Story and pictures on my blog at MySD300.blogspot.com

The STL builds a replacement fitting with a 1.6mm thick flange, 108mm outer diameter, and a 76mm diameter collar to fit into the opening in the shower floor.

If you need different dimensions edit the STEP file in a CAD package to create a new STL.