Kept on losing those little plastic clips that hold the secondary glazing in, couldn't find them for sale anywhere, so decided to print them. This fits fine for an Everest secondary glazing, aluminium frame. See the attached photo for how it's used.

Print on it's end (sample stl provided). 0.2mm layers, abs, no raft.
It's quite a precise print, but there's enough plastic to allow it to have reasonable strength. Note the asymmetry of the support cleat: That's to allow a bit of wiggle room depending on the window frame you have. I've also included the snippet of openscad I used: Only took a few minutes to generate this, and only 11 lines of code.