For the 1 1/2" Allchin, W Hughes described wrapping tinned copper wire around 1/4" rubber tube. He suggested grey tube, which is not common, and fuse wire, 10 or 15 amp, I forget which, but it's 0.015" dia or 28 swg.
His method was to wrap 3 lengths of wire side by side, then remove 2, to give the spacing.