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
Steel Machine Key 3/16" x 3/16", 3/4" long. These keys are economical with high strength and will fit 3/16" keyways.
This is the waterproof inspection LT2 Robot. It has flipper arms to help it climb obstacles and for better maneuverability. It is capable of wireless or tethered control. The tethered option includes a fiber-optic cable spool up to 1km long.