The best size that has everything. Everything is functional. Everything is just right! [Back guard standard equipment] A back guard is equipped as standard on the back of the bag, which is prone to deterioration due to interference with the vehicle body. You can adjust the position of the back guard by yourself. This is a device that prevents damage to the bag even if the interference location changes depending on the car model and installation location. *The manufacturer recommends the use of saddle bag supports. [Hang base to avoid turn signals] When choosing a saddle bag, one thing to be concerned about is interference with the turn signals. This product's ``turn signal avoidance hang base'' does not require you to relocate the turn signal in order to attach the bag. [Not too small and not too big] The best balance of size with a capacity of 17L. If the bag is large, you may lose balance or rub the bag on curves. On the other hand, if it is too small, the capacity will decrease. The NB-100 was designed with the goal of being able to be mounted on any bike without sacrificing capacity. [PET bottle holder] The holder that holds a 500ml plastic bottle is removable. It can be attached to either the left or right side of the bag depending on the situation, such as solo or tandem.