Dyna Glide ModelsSuper Glide, Super Glide Sport, Super Glide Custom, Dyna Glide Convertible, Super Glide T-Sport, Dyna Glide Police, Dyna Switchback, Low Rider, Street Bob, Fat Bob and Wide Glide.
That is an anti-boredom toy for long rides. When used properly, you amuse yourself trying to adjust it to hold a steady speed, regardless of hilly terrain. This is accomplished by tightening it then overspeeding, loosening it and readjusting, tightening it then underspeeding, loosening it and readjusting, tightening it then overspeeding, loosening it, etc. Pretty sure my '05 Sporty had one and my '04 LR certainly has it.