SR-02Work out what the wall is made ofRun a stud detector or a small magnet over the marked line. A line of regular metal hits every 400-600mm usually means screw heads holding plasterboard to timber or metal studs; drag a magnet slowly and a strong, sharp pull means metal studs, while timber gives a weaker, wider signal from the screws only. Knock along the wall — solid brick or block sounds dull and solid everywhere, dot-and-dab sounds hollow between the dabs and solid over them, and lath and plaster has a slight give and an uneven, ribbed feel. If you're still not sure, drill a 3mm test hole in a spot the bracket will cover: pale, fine dust means plasterboard or plaster, coarse orange-ish dust means brick or block, and shiny metal swarf means you've hit a stud or its fixing screw.