There are a few options you can use to produce your UKROC rocket for the 2025 competition. The lower tube should be no greater than 57mm in diameter (BT-70). So good options would be either BT-70 airframe, 50mm Klima airframe or LOC 1.9" (49.5mm OD) airframe. For your upper tube this must have at least a 60mm inside diameter. So you could choose a BT-80 airframe, Klima 75mm tube or LOC 2.56" (65mm ID) airframe. We offer transitions for all of these tubes to interface with each other as well. We've included a selection of the body tubes that we feel should cover almost all builds here. If you can't find the tube you're after then please check out our full section here.
In terms of strength we find the Estes "BT" tubes to have the thinnest walls, the Klima tube is a bit stronger, and the LOC cardboard tube is the strongest of all. Phenolic tube from LOC / PML or Black cat is even stronger but probably is over specified for the UKROC challenge and will introduce unnecessary weight in our opinion.