# Parallel Axes

A parallel axes joint is a four degree-of-freedom primitive constraint. The constraint is imposed such that the Z axis of a reference marker on one body (Body 2) remains parallel to the Z axis of a reference marker on the other body (Body 1) connected by the joint. All three of the translations are free along with one rotation about the Z axis of the marker defining the joint orientation. Joint primitives like parallel axes joints may not have a physical existence. Parallel axes joints can be used to impose unique constraints where using a regular joint would not be possible.

1. If the Joints panel is not currently displayed, select the desired joint by clicking on it in the Project Browser or in the modeling window.
The Joints panel is automatically displayed.
2. From the Connectivity tab, click Body 1 and pick a body from the modeling window, or double-click Body 1 to open the Model Tree (from which the desired body can be selected).
Note: If the selected joint is a pair entity, first distinguish between the Left and Right tabs in the panel, and then edit the properties. When defining a pair joint, use pair entities for Body, Origin, etc.
3. Similarly, click Body 2 and select the desired body from the modeling window (or use the Model Tree).
4. Click the Point collector (under Origin) and select a point from the modeling window, or double click the Point collector to open the Model Tree (from which the desired point can be selected).
5. Specify the properties of the axis that defines the constraint of the joint .
• To use an axis, select Normal from the drop-down menu, specify whether to use a vector or a point which points in the normal direction of the constraining plane, and make your selection in the modeling window or the Model Tree.
• To use a plane, select Inplane and specify a combination of vectors and points from the modeling window or Model Tree.
Note: Global axes can be used for vectors by clicking on the desired axis (x, y, or z) in the modeling window or by browsing through the Model Tree.
If editing a compliant joint, see Edit Compliant Joints or Bushings. To edit user-defined properties, see Edit User-Defined Joints.