This is your normal, everyone needs and therefore everyone should have it PTFE tube. Will work for 1.75mm filaments and 4mm couplers. The internal diameter is a little larger to allow for more room for your filament. While the supplier advertises these at 2.5mm, our measurements show a diameter of 2.35mm.
This tube is great for ERCF!
Order these by the meter (e.g. quantity 2 = 2 meters) I can cut these however you wish though, so if you want special cuts of your tube please place a note when checking out.