plasterboard screws

Do The plaster board fixings that screw directly into the plaster board and allow you to then screw into them come in different sizes.? Have shelf that has plug etc but would prefer to not have to drill but the screw of the shelf seems a bit small

I think I know what you mean by plasterboard fixings - the ones with the big fat auger-type screw with a finer (4 or 6mm) threaded machine screw in the middle?

I've only ever seen one size, but two types of material. The plastic ones are junk, the die-cast aluminium ones are OK-ish. Can you use toggle fixings? They're much much better, but a little more fiddly to use.

I'd try find timber if I were you. Those plaster screws/plugs don't hold much weight. Plaster board is not design to support things. sometimes its better to fix a board to the wall where you can find wood. Then fix the shelf to that.