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These should expand / contort when screwing in, the secure to the back of the plasterboard. Emphasis on ‘should’.
In my experience, they are flimsy at best and fail at worst.
If you’re installing shelving (assuming you’re putting heavy things on them) I would go with hollow wall anchors (don’t forget to buy a setting tool…).
If these are external walls or internal supporting walls, you’ll lively have dot and dab which means the space between the plasterboard and brick / breeze block will be small. You should drill into the brick to accommodate the tail of the anchor.
Installing string shelving onto plasterboard walls, attachhed is photo of the screws and plugs they supply
2a. do i need shorter screws with matching head shapes to the provided ones?
2b. do i need to drill the brick behind and use the provided ones?