Now is probably not the time to mention "weld nipples" . . .So 2x 3 mtrs of best 3/4" PSP taper threaded at both ends steam pipe costing total of £43 inc. VAT later and some judicious use of a hack saw I now have 2x 1.2 m lengths of tube for the door width size clamps and two at 1,8 lengths for the other pair of clamps. Plus I have two female tube connector sleeves as well
That BSS place is an amazing store of all things pipe in steel , brass & copper to about 150 mm in diameters as well as a myriad of other really hard to find high quality engineering supplies .