Against high wound plastic rectangular box section Confront Credential Oxidize
Trebork - Rectangular Tube Inserts Plastic End Plugs, Black, Grey & White
Plastic Tube Insert Plugs, 12PCS Rectangular Square End Caps Black Plastic Inner Plugs Pipe Tubing Post End Cap for Box Section Rectangle Tube (40mm*80mm) : Amazon.co.uk: DIY & Tools
4Dmodelshop - Plastic square tubes
101x81x23mm clear container - Watkins & Doncaster
Rectangular Hollow Section steel 75mm x 50mm x 3mm