Amazon.com: Prescott Plastics 1 1/2” (38.1 mm) Square Plastic Plug Insert, Black End Cap for Metal Tubing, Fences, Glide Protection for Chairs and Furniture (10 Pack) : Industrial & Scientific
JOHN GUEST SpeedFit 3/4 in. CTS Pipe Insert Fitting (25-Pack) TSI28 - The Home Depot
Plastic Insert Tees – Merrill Manufacturing
LASCO 17-0911 1/4-Inch Hard Plastic Tube Sleeve and Insert Kit, 4-Piece - Pipe Fittings - Amazon.com
Amazon.com: Prescott Plastics 1.5" Inch Round Plastic Plug Insert (10 Pack), Black End Cap for Metal Tubing, Fence, Glide Insert for Pipe Post, Chairs and Furniture Legs : Industrial & Scientific
3" PVC Pipe Insert Adapter (Insert x Spigot) (White) - The Drainage Products Store