They are metal. In the shape of the letter L. Each has 4 holes. Pretty easy actually. They could only be better if they come with a discount.
Stainless Steel Bracket Shelves: Industrial Hanging Hardware
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π© N100 792 National Hardware Plated Holder
Stainless Fastener Bracket for Furniture Bedframes
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π Enhance your Woodworking Projects with KREG P PIN Solid Wood Pocket Hole Plugs
High-Quality White Plastic Flush Type Plugs for Industrial Hardware Applications
π 50 Pack of P MAP Maple Pocket Plugs
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π Kreg P OAK Plugs Pocket Hole 50 Pack