I have used gears from the toolbox in my design and modified them slightly. I used 'save as' to save it seperately. This seperate file, I've used in my assembly. But a lot of time it happens that when I open the assembly the modifications dissapear and the tree shows the files from the solidworks tools library and not the files I saved. I replace the files with the ones I saved and everything is back to normal. But the next time I open the file, its the same thing again. What am I doing wrong? What is the correct procedure to edit and use parts from the tool library?