Edge select mode is used to select pairs of vertices which are adjacently connected within a face. An [i]edge[/i] is not an actual unit of data in a Stem3D mesh, and has no associated attributes or properties; it is simply any pair of vertices with the necessary connectivity.

When in Edge select mode, edges are hit detected in a capsule-shaped radius around the line formed by their endpoints, prioritized by their proximity to the cursor. Edges fully obscured by faces cannot be selected with the mouse unless the mesh is being displayed in [link=wireframe]wireframe[/link] mode. If the mesh is not in wireframe mode and the mouse is over a face, edges belonging to that face are prioritized for hit detection, even if other edges are closer to the cursor.

Clicking the [!keybind]left mouse button when an edge is moused over will deselect all other edges and select that edge. Holding the [!keybind]Shift key will toggle the selected status of the moused over edge. When an edge is selected/deselected in Edge select mode, face corners on both sides of the edge will also be selected/deselected. Face corners associated with adjacent faces not straddling the edge will either be affected or unaffected depending on whether [link=inclusive_mode]Inclusive Mode[/link] is active.

Holding the [!keybind]Alt key while in Vertex or Edge select mode allows edge loops to be selected. An [i]edge loop[/i] is a continuous chain of edges that pass through 4-way intersections at face boundaries. An edge loop terminates when it reaches its starting position, or an intersection that is not 4-way. When bordering a hole in the mesh, 2-way intersections are sufficient to continue an edge loop. The entire chain of edges to be selected will be highlighted on mouseover if [link=show_mouseover]Show Mouseover[/link] is on.

If the [!keybind]Ctrl and [!keybind]Alt keys are held, a subsection of an edge loop can be selected, extending from the most recently selected edge. By default, if the subsection is within an edge loop that would complete a circuit back to its starting point, the shorter of the two paths around the loop will be preferred. To toggle between the short path and the long path, while still holding [!keybind]Ctrl and [!keybind]Alt and keeping the mouse over the edge to be selected, either [!keybind]scroll with the mouse wheel, or press the [!keybind]semicolon key.

Pressing the [!keybind]Tab key in Edge select mode will cycle through all edges in the mesh. The order of the cycle is determined by face order. Holding the [!keybind]Shift key will cycle in reverse.