You will probably require around 4 Supports For an average length of shelf the more supports you add the more weight the shelf will be able to
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16 X Clear Shelf Supports Pegs With Safety Catch for Upto 6mm
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5mm Metal Shelf Support Studs Pegs M5 Kitchen Cabinet Cupboard
12 METAL SHELF SUPPORTS PINS PEG PLUG IN 4,5,6,7MM HOLE KITCHEN CUPBOARD CABINET
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STRONG METAL SHELF Support Plug In 5Mm Stud Pins Pegs Kitchen
Shelf Supports Pegs PINS Plug Stud 3mm 4mm 5mm 6mm 7mm KITCHEN
50 Pieces Shelf Pegs Pins Fixed Table Shelf Bracket I Shape Metal Shelf Support Pins Set for Cabinets Bookshelf M68E - AliExpress
9 X 5mm Metal Shelf Cabinet Studs Supports Pegs Kitchen Cupboard