To add a component into SolidWorks Toolbox Library you can do the steps below:
1. Prepare your component, must save as SolidWorks file if the format is imported from other CAD.
3. Select the Toolbox at Taskpane and right click at any empty place. Select Configure…
4. Select Customize your hardware
5. Right click the Toolbox Standards and select New Folder to create new folder to store all your customized hardware.
6. Right click the newly created folder and click Add File… to select your customized hardware.
7. Configure the hardware as you like and you can use it on your asembly! (If you didn’t see your hardware, try to restart your SolidWorks, then it should appear).