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
This ATR robot uses custom length sides, a custom top cover, and 10 inch traction lug tires. We have included everything to make it ready to run including batteries, controllers, chargers, etc.
SparkFun's minimal design approach to Arduino. This is a 5V Arduino running the 16MHz bootloader.