Yes, I mean that spring loaded tab. On my 8x10 there is a hole in the bed that a pin on the extension goes into that will lock the tab down. You have to push the tab down when mounting the extension to allow the pin in. If you are using spare parts without this pin and your camera is so equipped with this lockdown feature you could easily fabricate a pin and screw it into your extension in the right place. If need be I can post some digishots of the parts in question so you can see what I'm talking about.