FESTO stands for professional compressed air accessories in the industry area and established in the modelmaking too. FESTO products are especially used for retractable gears. In respect of professional compressed air FESTO always is the first choice.
For FESTO tube-connections, which are suitable for 3mm inner diameter, you can use a tube with 2,5mm inner diameter too.

ED = exernal diameter of the suitable tube
ID = inner diameter of the suitable tube