Those are called 'hubs' and the holes for the spokes - eyelets.
Through the center of the hub you will find the axle-spindle, unless someone removed it. To get to the axle-spindle you would need to disassemble the hub, as if for an overhaul. There is a large amount of space dedicated to how-to a hubset,
Originally Posted by Cateye
Only panthers007 is stupid enough to believe that this is a good idea.
A. Body Straightness
B. Machining Straightness
C. Cup Straightness [Extremely Important!!!]
A1. This assumes same size flanges on each side. Roll hub on flanges on chalk, etc. If perfectly parallel lines are created - no flaring out or in. STRAIGHT
A2. This assumes unequal flange sizes. Place hub in truing stand. Bring truing guides all the way up and bring points to within 1/8" of the flanges one at a time. Rotate hub. If flanges rotate perfectly - or both deviate a tad at the same time... STRAIGHT
B1. This test doesn't mean the hub is bad. Place hub in truing stand. Rotate. Does one side or both sides rise and fall during rotation. About 90% of all freewheel hubs will do this...about 10-20% of freehub equipped hubs will do this. If present, even when extreme, it has very little impact on shifting or chain drop - despite common myth.
C1. Adjust hub so that it has a slight grind. Turn hub several times. Does it bind in 2 or 4 places consistently? If yes...
- Unlock cones.
- Hold hub vertical.
- Remove top cone...clean grease around the outer 2-3 mm's of the edge of the body so you can clearing see the entire circumference of the cup edge.
- Turn the hub...does the cup turn flat...or does the cup noticeably rise and fall at certain points in excess of a couple millimeters?
- Put cone back in.
- Turn hub over...repeat the above.
If a cup rise and falls more than 2mm during rotation...
- Higher end hubs such as old Campy SR's and NR's can be salvaged with a press in a machine shop.
- El Cheapo generics...toss 'em. Don't even try to save 'em...don't even try to use 'em. They will grind out prematurely in the binding locations...for every 10 I import from Taiwan...I have to toss out on average 1 hub shell. (One way to build a supply of spare axles, cones and bearings...)