This is the Rotary/mechanical speed control from Traxxas.
This is a Stock part for the:
1/10 Stampede 2wd (Mechanical Speed Control) #3606
Features:
Comes with a 47uf capacitor pre-installed on the motor leads.
Includes:
One (1) Rotary speed control unit with resistor
Two (2) Ball connectors(two ball ends and two pivot balls)
One (1) 2x21 threaded shaft
Two (2) M3x15 machine screws
Two (2) 3x6mm aluminum washers
Two (2) M3 lock nuts
One (1) M2 Nut
One (1) On/Off switch case w/switch cover
One (1) Servo Horn