The configurations differ in the location of balls (red) and their preload springs and in the location and number of adjustment knobs (green).
There are 3 binary choices, yielding 8 configurations. Each configuration is designated by a 3-character model number suffix. For example, "M6025-6DL".
The M6025 positioner is comprised of a stationary base (light gray) and a moveable J-arm (darker gray). Three screws (green circles) control tilt, tip and focus. To adjust only focus, you must turn all 3 screws by the same amount. For a vertical interferometer axis, the 3 screw knobs are best located below the positioner so that the moveable weight is resting on the screws instead of hanging from the preload springs.
All models have 3 balls (red) that constrain centration and clock. For a horizontal interferometer axis, the best orientation is as shown with 2 balls below the arm. If you need the optic axis to be lower, then an orientation 180° different, with 2 balls above the J-arm, is acceptable. Less acceptable is 1 ball below the J-arm. You should especially avoid orientations with 1 ball above the J-arm.