A brake for a trolley which travels atop a zip line is presented. The brake includes a brake body having a brake body with a top plate and two side plates extending downward from the top plate, the top plate having an underside which faces the zip line. One or both of the side plates may contain an aperture for accepting a rigid member which secures the trolley to the brake body. A brake pad is preferably positioned on the underside of the top plate. Exemplary embodiments may contain a brake extension which connects with the brake body and extends downward towards the user.