Anchors are used to define the location of an object dropped from the catalog, and also for animation options. Anchors have the standard 3 Axis system, with XYZ, or width, length, and height. Anchors are available at multiple levels, for example Assembly, Part, Shape, Profile etc. The level of Anchor you customize will only affect that level, not the other Anchors at the various other levels of the item.

‍Tip: if you drag and drop an item from the catalog and it comes in upside down or sideways, it is likely because of the Anchor position. You can adjust the Anchor position by selecting the object, then clicking on the Anchor and activating the TriBall (with the Q key or F10 key). You can then rotate and reposition the Anchor, and try dragging back into and out of the catalog to see the new behavior.

Drag Positioning Behavior (Interaction Properties)

Each shape, as well as each part, has an anchor that serves a variety of functions.  One function applies to a shape’s drag positioning behavior options, as follows:

• Drag freely in space.  This option allows a shape complete freedom of movement, whether it is on the surface of another shape/part or an independent part.
• Drag along surfaces.  With this option, an added shape or part can only be repositioned on surfaces of its base shape or part.  However, if you move the base, the added part or shape will not accompany it.  This behavior is indicated by a horseshoe magnet icon displayed beside the anchor.
• Attach to surface.  This option is similar to "Slide along surfaces" with a couple important differences.  First of all, this   behavior is only available for shapes and is the default for shapes dragged in from the catalogs and dropped on existing shapes or parts (Note: This is not available on features of Structured Parts. Structure Parts will define relationships in other manners).  As with the previous option, movements of an added shape are restricted to the surface of the base shape or part.  However, with this option active, if the base is moved, the added shape will remain attached and move with it. The icon for this behavior is a horseshoe magnet with sparks emanating from its ends.
• Disallow Drag.  Use this option to fix a shape or part at its current location in the scene.  The shape or part cannot be dragged to an alternate location.  The icon for this behavior is a push pin through the anchor point.  This is the default drag positioning behavior for a base shape or part.