DANKE 5 I purchased this for the leaf spring inside. Last year my left mouse button started to fail, this year its the right. Last years version had a single piece leaf spring that was the same one used in my Logitech G5 mouse and it dropped in exactly. This years version has a 2 piece leaf spring that needs to be machine fit. If you're buying this to fix a failing mouse you'll need to de-solder and replace the entire unit.