How the torque at any point in. Its plane is constant.

torque is the combination of force applied at a point with the right angle (perpendicular) distance from that point to the axis of rotation (in our case, this'll be an axle). The formula to compute torque is simply this:

T = F * d, where
T = Torque
F = Force (here, the force applied perpendicular to the axis)
d = Distance
Hence Torque will always be constant at a point in its plane.