This is a 9V battery clip typically used for our wireless cameras. The ID is 2.1mm, the OD is 5.5mm. Center positive.
9V Battery Snap with 12" Leads
100 pack of black UV resistant nylon with flexible tape section, pull tight and does not come undone. Length 11 inches.
Steel Machine Key 3/16" x 3/16", 3/4" long. These keys are economical with high strength and will fit 3/16" keyways.