Width = 6mm
Pitch = 2mm
Length = 5 meter
The GT2 belt/pulley combination is the best solution for linear motion. The older T2.5 system was designed for one-way movement only and therefor has significant backlash on the two-way movement needed in 3D printers. The GT2 system has rounded notches that operate more quiet and smoother. The GT2 was specifically designed for two-way movement and has zero backlash.
The 5 meter length is enough for a Kossel XL or a Kossel Mini.