This is a replacement end cap for a Swingline Optima stapler, in case the original has become damaged.

Print with organic supports and a brim.

Salvage a spring from a clicky pen, and insert it into the hole on the bottom. Then FORCE the entire part into the hole on your stapler. (I should have made one more pass and improved the retention tabs) then press it until it moves freely.

Beware, you have to destroy the part to get it back off your stapler.

The spring mechanism of the staple tray almost has enough force to kick this back up, but not quite.  The spring from the pen ensures it won't stay down.