Excellent design, as usual. I have printed 8 so far, and all of them open and close very smoothly with an extremely satisfying click. For springs, .4x5x10mm work best for me. I converted 4 to switchblades and unfortunately none of them will open with a press of the button. The rubber band doesn't even seem to help until the blade is 90% open and then it snaps open that last 10%. Plus it just makes closing the blade more difficult. Used the same rubber bands as in a few of your other designs, all of which work flawlessly, so I'm confused (side note, I was able to double one of them up, which took a while, but still did not work). Finally, I used my pen sander to smooth out all points of friction I felt could be hampering it, then I put a drop of Super Lube 51004 around the pivot, but same result. All that said, since the switchblade is just a mod/tweak of the original design, I can't knock off a star. Does exactly what the original design says it does and does it with great style!