DELSEN 100 pcs Metal Shelf Pegs 5 x 16mm Shelf Support Pins Studs for Brackets Kitchen Furniture Cabinet Bookcase : Amazon.co.uk: DIY & Tools
2 in 1 Bookshelf / Peg Rail Wood Bookshelves Peg Rail Wood - Etsy UK
All About Shelf Supports
3 Styles Of Metal Shelf Support Pins Including L-shaped Brackets / Flat Spoon Style Shelves / Cylindrical Shape Shelf Pins For Bookcase Cabinets | Fruugo UK
Uxcell 20/30/40pcs Shelf Bracket Pegs 5x16/25mm Stainless Steel Cylindrical Shape Shelf Support Pins For Cabinet Bookcase - Pins - AliExpress
IKEA Billy bookcase tip: if you have an OLD Billy bookcase (pre-2014) you can still add extra shelves even though the new extra shelves from IKEA use a new, disc-shaped shelf pin.