I have a tekna micro knife I got on Ebay. When I got it the sheath wouldn't retract, however I found the blue prints on the web and as it turns out there is a "Y" shaped gray plastic spring inside that got all bent to one side. I took it apart and reshaped it with a heat gun and some ice water, works like a charm now and it holds an impresive edge.My only gripe is that the pocket clip is at the top by the button so I find it doesn't sit well in my shirt pocket, It tends to slide around, so it sits ontop of my desk in my "IRON CHEF" coffee mug to open letters. It is fun to play with though. Check Ebay I see at least two of them sell a month.