For 22mm handle bar diameter (Grip diameter 30-40mm)
"Throttle control" . A clever Taiwanese invented and patented this little helpful part.
The matter is quite simple: Once the desired speed is reached, the lever is pressed with your index finger against the brake lever. The right hand can let go (not for phone calls please ...) or at least be relaxed on the throttle, because this not turning back. To "disable" just turn the throttle back .
Hard to describe, check it out here.
In the U.S., this is already a hit.