This is a replacement for the plastic restrictors on sash windows.  They allow you to leave your windows partially open, but children can't open them wider to get out (nor burglars to get in).

First, print the Sliders in PETG, 0.2mm layer height, 3 perimeters (PLA is too brittle).  To print without supports, stand them on end (see the .3mf).  Print more than one at a time to allow cooling between layers.  I used a brim to aid bed adhesion.  Include one Pin Helper in this print.

Print the Spring in very flexible 30D or 40D TPU (81A-91A).  Stiff TPU (95A or 98A) permanently deforms when compressed and doesn't provide enough ‘springiness’.  

Use the little Pin Helper tool to squeeze the spring into the Slider and insert sewing pins through the holes to keep it in place. 

Now, print the Cases (in PETG, 0.2mm layer height, 2 perimeters). Add a a *pause at 12.2mm (included in the .3mf) and reslice.  When the printer pauses, drop the sliders with springs into the open Case.  Make sure it is fully in and set down flat.  Resume the print to finish closing the top of the Case..

Promptly remove from the print bed and pull out the pins so the spring doesn't permanently deform in the heat. Slide the slider down until it pops open.  It make take a minute for the sprint to fully decompress.  Insert into the slot in your window.

*To add a ‘pause’ in the print, slice the Cases,  move the layer slider to 12.20mm, right-click on the ‘+’ and select ‘Add pause print (M601)’. Reslice.