VEVOR Industrial Pipe Shelving, Pipe Shelves with 3-Tier Wood Planks, Rustic Floating Shelves Wall Mounted, Wall Shelf DIY Bookshelf for Bar Kitchen Bathroom Farmhouse Living Room, 43x38x11 inch

If you are referring to expansion tube, then our answer is 6mm drill bit.

This is described in detail in the user manual, which you should review:<br/>https://d2v0huudrf11kh.cloudfront.net/16225108815801.pdf