I use this to plug the end of a 2x4 aluminum tube. They fit snugly in the channel, but the cap doesn't completely cover the material, leaving sharp corners exposed.
WIDGETCO White Hole Plugs
9 Review
π 50 Pack of P MAP Maple Pocket Plugs
7 Review
π Kreg P OAK Plugs Pocket Hole 50 Pack
High-Quality White Plastic Flush Type Plugs for Industrial Hardware Applications
Stainless Steel π© Fastener Hardware by BIGTEDDY
π§ Boeray Stainless Steel Straight Brackets Mending: Durable and Versatile Support Solution
8 Review
Stainless Fastener Bracket for Furniture Bedframes
Stainless Steel Bracket Shelves: Industrial Hanging Hardware