A bass trombone-with an F attachment only
There are also bass trombones with only a single valve and F attachment installed (the Yamaha model in YBL-421G). The tube length of a bass trombone with only an F attachment is the same as that of a tenor bass, and both instruments are able to play the same range. However, the bass instrument has thicker tubing, and therefore can more easily play in a lower range than a tenor bass trombone.
On the other hand, a bass trombone with two valves has a longer tubing than a tenor bass, giving it a wider range.