Joints in the model can have a single component of their position set to a specified value so as to align the joint to a specific location.  To align a number of joints to the same position

§    Select the joints to be aligned in the Frame window

§    Choose Align Joints… from the Advanced submenu in the Geometry menu

A dialog box will appear prompting for the axis and position along that axis to which all the selected joints will be reposition to.

§    Select axis to which along which the joints will be aligned

§    Type in the values for the new coordinate

§    Click the OK button

Upon successful exit from the dialog all the selected joints will be have the specified coordinate set to the new value.