These are the larger width balloons for twisters. They are 3″ wide and 50″ long. The Q stands for Qualatex, the make of balloon.
These balloons are idea for large models. You will not get many twists out of a 350Q due to the size of the bubbles. It will take about 3 balloons to make a regular dog, but it will be an enormous model. Great when working on stage, or where high visibility is required. If you want to make a big impact with a booker, then use these, but practise your models with them before you perform, as they are more difficult to work with.