It took me a bit to figure out that you are customizing the Ribbon. I'm not sure if you want a Quick parts button on your custom tab of the Ribbon, or something fancier. To add the Quick Parts button to your custom tab of the Ribbon, in the Customize Ribbon category of Word Options, use the 'Choose Commands From' drop-down and choose 'All Commands'. Then you'll find the Quick parts command. It's sneaky and hard to find unless you go to 'All Commands'. Is this what you are trying to do?