Indexed switches mounted on the down tube.
Although the combined brake shifter has become the norm in racing bikes, they are still sold in the cheap segment on bicycles with indexed switches on the down tube (fig. 48).
The indexed switch is structurally almost identical extending between the handle and the fixed part with a plate cam is where a pellet incident.
As a result, the switch has fixed positions.
The friction increasing between the fixed portion and the lever is to change the switch in a normal friction commander.
This may be necessary if the index system is not functioning properly.