Electrical – How is this junction box intended to be used

Method 1

1. Place the box where you want it and screw it lightly to the stud.
2. Run the clamp screws in until they bite into the wood.
3. Remove the box.
4. At the marks left by the clamp screws, drill 1/4 inch relief holes about 1 inch into the stud to make room for the ends of the screws
5. Reinstall the box.

Method 2

6. Remove the existing clamps
7. Knock out the inner discs on the sides (not the ones near the original clamps) by pushing one side with screw driver, then wiggling back and forth until it breaks off
8. Install bolt on cable clamps like these (screw section goes on the outside)

250.4(A)(2),(3), & (4) says that "Normally noncurrent-carrying conductive materials enclosing electrical conductors or equipment" should be grounded and bonded. So while you may not have to connect the equipment grounding conductor to the box, the boxes do have to be grounded and bonded. Since you're using EMT, the boxes can be grounded and bonded via the conduit. If you were using nonmetallic conduit, you'd have to ground the boxes some how.