This is a flywheel cage for use in Nerf blasters, intended as an afterburner cage. Sourcing wheels has been difficult, but the cage design is here, open-source. The newer design has a bit of extra cage diameter capacity for 2-3/8" wheels.
Posting this for my Nerfer friends.
Wheels and hubs can be bought from BaneBots:
Wheel, 2-3/8" diameter, 50A durometer rubber tread
http://www.banebots.com/product/T40P-245BA-HS4.html
Hub for T40 wheels, 2mm shaft attachment:
http://www.banebots.com/product/T40H-SM21.html
Note: The hubs have been discontinued and are on closeout, and an additional nylon press-fit bushing is needed, 1mm ID, 2mm OD. Shouldn't be too difficult at all.