The procedure is the same for the 3 blade. There are 2 ways to use the metal hubs. You can use one hub on the outside of the supports. This make a space of about 5/8" between the hubs and requires 2 hub to shaft adaptors and a longer shaft lingth but its very strong this way.
The blade is pictured with both metal hubs resting together. This has worked fine in wind of 60 mph no problem but in a high wind area I'd go the stronger rout.
The hub to shaft adaptors come in the following shaft sizes 1/4", 5/16", 3/8", 1/2", 5/8" and 3/4". If you have a metric shaft just pic a smaller size and drill it out.
These blades have done 63 watts at 5 mph, 1200 watts at 45 mph and survive 80 mph storms.
JK TAS Jerry