These alligator clips are useful  for smaller wires that you don't want to deform. The clip has smooth  flat metal blades that clamp down on the wire, making for a good  connection to thinner wires. There are strain relief crimp points and...

This is a 9V battery snap with barrel connector, works perfectly to add a 9V battery to your Arduino USB board. Center-positive 5.5x2.1mm barrel connector.