My C-150F uses a nylon or fiberglass front bulkhead which “floats” inside the spinner dome. It has a lip that fits inside the front of the prop to maintain alignment. When the nylon bulkhead no longer fits tightly, you may need spacer rings between the front bulkhead and the front of the prop to preload. Some owners have added material to this floating bulkhead to return it to its original dimensions. Take care of this plastic bulkhead as it is very expensive.
Yes, on some aircraft, the front metal bulkhead is riveted to the spinner dome (C-172, C-175 and some C150’s). The rear (aft) backing plate (between the prop and the crankshaft flange) is not riveted to the spinner dome unless the spinner dome is a two-piece design (probably never).
If a metal bulkhead is bolted to the front of the propeller, then neither the front nor rear bulkheads can be riveted to the spinner dome (my opinion). Phillips head machine screws are used here. If the prop has six bolts, and the front bulkhead has eight screw holes, align everything up before tightening the prop bolts.
I’m not an engineer, but I think that if the spinner wobbles or vibrates, it will crack the rear backing plate. When the front bulkhead is properly installed, the screw holes in the rear bulkhead should be only partially visible before installing the screws. You should see about one half (the front) of the threaded opening. Gently push the spinner towards the engine about 1/16” and insert the screws around the spinner until all are started. Tighten evenly around the spinner using several passes. Check alignment by turning the prop against a reference.
Use all new screws, of the same type and length, as propeller balance may be affected. No need to over tighten if the nutplates are doing their job. I like to use AN525 Washer Head structural screws as the smooth grip portion does not tear up the aluminum spinner hole like fully-threaded screws will. A thin nylon washer will save the paint. See Genuine Aircraft Hardware Reference book, page 28.
If you don’t put it together correctly, you get El Bondo de Swordfish:
