The Vandoren 13 Series Profile 88 Bb clarinet mouthpieces are a model that was developed specifically for playing at A=440Hz.
With this lower pitch the mouthpiece is able to resonate in a different way than the standard range (442 Hz), creating different tonal colours.
The concept, developed in 1994 for the UK and American market, or any region that tunes to A=440hz.
The 5RV mouthpiece was the original design of Robert Van Doren and his own personal favourite. It is widely used by classical players: Tip opening is 1.065mm with a medium-short facing length.