Misplacing a back cap wrench is certainly not hard to do. Many will attempt to use pliers and other tools to replace their back cap wrench, but without extreme care, cap will be damaged. It’s best to just contact your dealer for a replacement. If that’s not an option, or your dealer wants some obnoxious sum for one, you can probably find a suitable replacement here. Many back cap wrenches, such as the one pictured, will work with multiple handpieces.