Beringer
 Thumb Brake with 14.5, 17.5, or 20.5mm  pistons are ideal to control the rear brake on 
any 1, 2, or 4 piston caliper application. Can be plumbed directly to the 
rear caliper and will require a dual banjo bolt on the caliper.
It can also control a single 1, 2, or 4 piston front brake caliper.
When
 the rear brake pedal is still required, the Beringer Thumb Brake will 
need to be paired up with Beringer's MC127 floating rear master cylinder
 which has special piston cups allowing it to receive hydraulic pressure
 from the Thumbrake and to send hydraulic pressure to the rear caliper 
as well.
Dual calipers applications such as for stunt bikes require a larger bore size. Please Inquire.
Beringer Thumb Brake is photographed upside down here to show hydraulic connections.