This A/B is arguably the best available. It is True-Bypass, solidly built, properly grounded, and very good looking. It works well to switch between two amps, and also works well as a Tuner Mute. Bleed free, buzz free, and pop free.
The A/B uses the "B" size enclosure. It measures 4.4 x 2.4 x 1.0 inches; 11.3 x 6.1 x 2.5 cm.