Z72 B 08 Tooth Sprocket 1/2" ID 5/32" keyway No Set Screw

Z72 B 08 Tooth Sprocket 1/2" ID with 5/32" keyway, No set screw, 7/8" wide hub.  

Use Z72 Chain 1/2" x 3/32".

You could use one or two 1/2" ID shaft collars to hold in place or snap ring grooves.