You wil need two snaps, these are like a punch as you can see in my pic above but they have a hemispherical recess that the preformed head of a rivit sits in.
You put one snap in your vice, slip a rivit through your tee ring and spoke and then place it all onto the snap, a few blocks of wood to hold the wheel level helps. Next you “set the rivit” this is done with a homemade hollow punch that slips over the rivit shank and is then hit to make sure the two bits of metal are firmly together and the rivit tight upto the underside. The snaps that RDG sell also have the hollow hole but most are just like punches
Now the tricky bit you place the second snap onto the protruding end of the rivit and give it a few sharp blows, this will form a matching snap head as the rivit is formed into shape. In reality you will want to do quite a few practice rivits before you get an acceptable head and to determine how much rivit to have protruding (about 1.6 times dia) to get a good head.
If its going to be painted then you will find copper rivits fine for a 2″ balance plough as they are a lot easier to form than steel.
Jason