Square Plastic Conduit 100mm x 100mm x 3m - Ray Grahams DIY Store
Trebork - Rectangular Tube Inserts Plastic End Plugs, Black, Grey & White
ABS Plastic Pipe ABS Tube Square Plastic Tube, Suitable for Making Models and Decorations, 500 Mm in Length,Side Length:4mm(30pcs) : Amazon.ca: Industrial & Scientific