Tube? You mean the guide pin?
Short answer: Yes.
Long answer:
From left to right in your pic, you have:
- Caliper bolt, caliper, guide pin, dust boot, bracket.
The bracket bolts to the car.
The boot snaps onto/into a ridge at the bracket's guide pin hole.
The guide pin(s) should slide easily in and out of the holes in the bracket.
The caliper is attached to the guide pins by the bolts, so the caliper and pins can move as a unit, guided in a straight line by the pins in their holes.
If you're unlucky, a bad boot can let water get in, where it happily attacks the pin and the hole, rusting everything and likely seizing it solid. If that happens, the caliper stops moving properly and affects the braking at that corner. A common symptom is pads worn on a strange angle from the caliper twisting on the remaining good pin, or one pad worn down to nothing by a caliper that can't slide back.
If yours is stuck, you can either buy a new caliper assembly with bracket, try to find a used assembly, or maybe just a used bracket and/or pin, or try to unstick it.
Step one is usually to soak it with a penetrating oil of your choice. Pull off the boot and try to get the penetrant between the pin and the hole, so it can loosen the rust. You may be able to then just twist it out using big pliers or a wrench.
If not, next would be clamping the pin in a vice, and trying to twist the bracket off of it. Maybe try tapping the pin in a bit more with a small hammer to break the rust bond and get things started, then back and forth and pray and back and forth and swear and back and forth....
Next up would probably be heat. Propane might work, but a welding torch would be much hotter. As the bracket is a big heat sink, little "girly torches" might not cut it. Heat until bloody hot, then wrench on pin or pin in vice, and go for it.
If you manage to get the pin out, sandpaper and wire brush the living crap out of the pin and the hole, until everything is shiny clean. Test to see that the pins go in and out without any binding or excessive roughness, then slather it all with silicone brake grease and test again. If you're happy, reassemble and call it good.