The Galper register tube (shown on the right in the picture below) is an improvement over the standard straight register tube (shown on the left).
This is a discontinued product, but the web page for this can still be found at this address: http://www.mytempo.com/register.htm
From that web site:
The throat Bb has always been a stuffy note on the Clarinet due to the normal register vent being too short. Increasing the length of the vent internally creates problems. Avrahm Galper created a longer register vent by extending the vent outside of the body of the clarinet. This not only remedies the stuffy Bb problem but also makes the clarinet feel much more even-blowing in the upper register.
Uneven resistance for the Buffet Bb Clarinet is now a thing of the past.
The Galper Key/Tube was invented by Internationally known and respected, Avrahm "Abe" Galper. Abe was principal clarinetist with the Toronto Symphony for 30 years. Mr. Galper also served as principal clarinetist with the Palestine Opera Company, the Israel Philharmonic, the C.B.C. Symphony, the Toronto Philharmonic, and the Canadian Opera Company.
The Galper tube necessitates that a replacement register key will be used, which was also supplied with the product:
More information from the web site:
I'd like to try one! Silverio in Argentina makes an imitation of this.