This is for the Bemis NextStep2 toilet seat with soft close hinge.  It may fit other Bemis toilet seats.  It seems these hinges are prone to breaking.  This is what a broken OEM hinge looks like:

You'll want to use supports for the inside as shown (organic works great for this).  My toddler has broken 2 OEM hinges and one printed replacement already, so I'd suggest cranking up the walls and infill.

Changelog:

Rev2:  I've updated the model to better match the face profile and length of the original part.  I've also slightly decreased the angle leading up to the hinge which prints much cleaner and stronger.