Tubes or pipes with an exact inner diameter
When your project, like mine, needs a tube pipe to fit exactly around something, consider making your own. I could not find anything with the exact inner diameter to fit a 5 mm photo transistor. Or a 3 mm IR LED for that matter. So I decided to make some to my desired measurement.
I used paper that is used to cover books. It's strong and dark. Although IR is not absorbed completely, none will penetrate from the outside either. To provide exact measurement of the inner diameter, I used drill bits as templates.
I used wood glue, but paste (starch), wall paper goo or hobby glue will probably work just as well. Wipe the first few cm dry so your drill bit will not be glued in place. Roll up as tightly as you can. I discovered it is not necessary to use a drill bit larger than the intended ID. The pipe does not shrink as the glue hardens. It's not easy to roll the stiff paper tightly. My pipes came out a little loose around the steel templates.
Cut to length with a hobby knife or small hack saw. Here you can see the end result used in my project.