The set screw is metric. It screws into a groove machined in the shaft to prevent the wheel from pulling off unintentionally. If you have any questions as to whether it will brake loose, rotate the wheel so the screw is upright, make a little dam around it with childrens modeling clay, fill the dam with PB Blaster and let it sit for a few daze. With that, if you alternate between turning to tighten and loosen, it should break free. Patience is the rule. If the wheel won't come off easily, you can make an extractor with a couple of U-Bolts around the spokes at the hub and a short length of 2x2 wood passed through the U-Bolts and across the shaft. Drill a hole in the center of the wood block slightly smaller than a 1/4" lag bolt, flatten the face of the lag bolt where it will bear on the shaft, tighten the U-Bolts until the wood is flat against the shaft and then turn the lag bolt into the block. Works like a charm and won't damage the wheel
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."