This is an add-on armor piece that attaches to Volcanicus's left thigh. This upgrade not only provides a beefier appearance to the combiner but also adds a port into which you can insert a Prime Master or a Titan Master figure. Attachment of this upgrade is simple, all you need to do is line up the connecting tabs and plug it in! I hope you enjoy it! There is another companion product in my store that attaches to the right thigh. Don't hesitate to message me if you have any questions. And, thanks again for looking.