Why is the horizontal force only in the x and z coordinates

Why is the horizontal force only in the x and z coordinates from Engineering Mechanics, Statics-Beford & Fowler-5th edition? chapter 4 question 75

Solution

No, there will be a force component in y coordinate also.

but the moment due to that force will become zero. as the angle between the force component in y direction and the position vector joining slider to bottom will be zero. so sine of 0 = 0 so moment =0