On a Star Wars stormtooper costume, there are fake clasps attached to the armor. I used OpenSCAD to design this large greeble. On a costume there are 6 large greebles which attach to the thighs, shins and spats (around the ankle). There are 6 smaller greebles that attach to the forearm (x4) and bicep (x2). There are 4 small greebles that attach to the helmet. The small ones are 66.7% the size of the large ones. I've included the large sized file only which can be rescaled by slicing software to produce the small greebles.

I designed these for the First Order stormtrooper costume which appears in The Force Awakens and The Last Jedi. It may be possible to use these for other costumes but I don't know. The greebles can be heated with a heat gun and bent to match the curvature of the armor.