That is the drive wheel of a belt grinder or sander. The smaller end connects to the 5/8 keyed shaft of a motor and the large end drives the sanding belt.

Beam Style Coupling. an older version. Used to connect 2 same shafts. the holes you see with the threads are for set screws that hold in a keyed shaft(s) usually the are 2 different size shafts but sometime it's all one size. usually connects a motor & a gearbox together. you can find them at any industrial sales place or online. Grainger, Motion Industries, purvis bearing. company's line Love Joy, TB Woods & Martin Sprocket manufacture them

References:

http://www.lovejoy-inc.com/products/motion-control-couplings.asp

Reason:
Another opinion was accepted instead.

That is the drive wheel of a belt grinder or sander. The smaller end connects to the 5/8 keyed shaft of a motor and the large end drives the sanding belt.

References:

http://www.ebay.com/itm/4-Alum-Drive-Wheel-for-2x72-Knife-Belt-Grinder-Made-I...