Want to buy some bolt on hubcaps for 15" steelies.

I know there are 3 kinds of hubcaps:
1. Retainer wire/clip on (these ones are most likely to fall off)
2. Fake lugnuts that screw onto your real lugnuts
3. Use real lugnuts to fasten

For 2., do you need special lugnuts? How does it screw on?

For 3., is it safe? I was thinking if the hubcap is placed between the steel wheel and lugnut, the lugnut would not be able to be torqued properly.