This is a 20mm dia. press-fit pin I designed for use with a cardboard construction workshop at the Children's Museum of Pittsburgh. It works somewhat like the Make-Do pins, but without a locking mechanism.
The pins friction fit using the natural grain of the part as the grip surface.
Printed at .32mm in PLA. The largest layer thickness you can get with good layer adhesion would be best. Be careful with the first layer, as over-extrusion can cause the slot sides to fuse shut.