I bought some 16mm aluminium (to be precise, 15.8 mm or 5/8 inch diameter ) tubing from Gardening Naturally to replace the rusted steel tubing on some shelving. Very quick delivery and helpful customer service when I phoned up after discovering that I needed 16mm and not the 13mm I had ordered. The delivery included a brochure with lots of useful garden equipment, which although not cheap has a reasonable postage cost if you buy multiple items. I have now ordered some butterfly netting, pheromone moth traps and grease bands to hopefully protect my fruit against insects!