Bore .250". The T series is the standard for Tenor trombone. They are numbered from 1 to 6, with 1 being the smallest and 6 the largest. Bore .250".
The T* (STAR) series is the same as the T series except that there is no cylindrical section.
The T* models are somewhat more free blowing than the standard models. To be used with the Tenor Tops.