The folding knife handle was held together with 3/16" (5mm) rivets. The openings in both sides of the 3D printed folding knife handle and the steel blade were widened to match this diameter; the blade lock opening was also widened to accept another rivet of the same diameter.
Rivets are a great way to attach pieces together without leaving a bulky fastener. However, rivets work on compression and can crush your work if your material is soft.
crushed print - attempt 1 (above):
When using a softer material, it's a good idea to test your rivet on some scrap material to see the outcome. My first attempt at using the riveter was not successful, crushing one of the openings and causing the end to split. In another area the material was binding at an opening and caused warping along the length of the handle, making closing the blade impossible.
proper rivet - attempt 2 (below):
Small washers and a dab of superglue were used in between elements of the print/lock/blade sandwich, then a rivet was pressed onto both ends of the handle to secure both sides of the folding knife. With finesse, you can get the riveter to pop the rivets with a tight bond and without crushing your 3D prints. The type and composition of your prints will play a factor in this (a more rubberized ratio of printing medium will have a greater compression allowance).
If the rivets don't pop and snap off it's better to back off the rivet once it's tight enough and just trim it down with a rotary tool. More on this in the next step.