These tools had locking tools but no obvious way to unlock them once fully opened (you are supposed to only fully open one tool at a time, and half open another tool to release the lock).If someone fully opened all the tools on a handle they then got stuck open. If you weren't careful levering up the tab to release the lock it could get bent so it no longer locked. Looks like that has happened to your tool.Two ways I can think of fixing it:1 Drill out the rivet, remove the rivet, remove all tools, bend the locking tab down again to where it should be, re-rivet (or replace the rivet with a screw). This might be OK, or the metal in the locking tab may have been fatigued and won't have the spring necessary to function properly.2 Buy a complete replacement handle(s) from ebay ( I think I see them offered by people who bought spares when the Schrade factory in the US sold off everything).I hope you get your tool going again, it looks like it has the rare combo edge knife blade with small serrations (most of these tools had larger serrations on the knife blade).