When you extrude a profile in Fusion 360, the result is always a completely solid body. For many parts that is exactly what you need — a solid bracket, a gear, a mounting block. But for enclosures, boxes, containers, housings and many other everyday mechanical parts, you need a hollow body with consistent wall thickness rather than a solid one. You could achieve this by carefully extruding individual walls and combining them, but that approach is slow, tedious and difficult to modify later. The Shell tool is Fusion 360's dedicated solution for this problem — it takes a solid body and hollows it out in a single operation, leaving uniform walls of whatever thickness you specify and removing material from whichever faces you choose to open. It is one of the most useful finishing tools in the entire application and one that every Fusion 360 user should understand thoroughly. What Does the Shell Tool Do? Shell removes material from the interior of a solid body, leaving behind walls of a specified uniform thickness. You select one or more faces to remove entirely — these become the open faces of the resulting hollow body — and Shell calculates the remaining wall geometry automatically based on the thickness value you provide. The result is a hollow part with consistent wall thickness on all remaining faces, which is exactly what you need for enclosures, covers, trays, cups and similar parts. Shell is fundamentally a subtractive operation — it starts with a solid and removes interior material — which is why it is applied after the main solid geometry of a part has been established rather than at the beginning of the design process. When to Use Shell Shell is the right tool whenever you need a thin-walled hollow part based on a solid outer form. Electronics enclosures and project boxes that start life as solid extruded or lofted bodies are among the most common applications — Shell hollows them out in a single step. Decorative and functional containers like cups, bowls and trays can be modeled as solid forms and then shelled to achieve the desired wall thickness. Covers and lids that need to fit over existing components are easily created by modeling the outer form as a solid and shelling it to the appropriate wall thickness. Structural shells like car body panels and aircraft skins in simplified form are another application, though these often require more advanced surface modeling techniques in addition to Shell. Any time you find yourself thinking about modeling a hollow part by building individual walls and joining them together, stop and consider whether Shell can achieve the same result more efficiently from a solid outer form — it almost always can. How to Open the Shell Tool Go to Solid in the top menu and click Shell. There is no default keyboard shortcut for Shell in most versions of Fusion 360, but you can assign one in the keyboard shortcut settings under Preferences if you use Shell frequently. The Shell dialog is simple with only a few options, making it one of the easier advanced tools to learn despite being extremely powerful. Step by Step — How to Use Shell Step 1 — Build Your Solid Body First Shell is a finishing operation that works on an existing solid body. Before opening Shell, build the complete outer form of your part as a solid body using whichever modeling tools are appropriate — Extrude, Revolve, Loft, Sweep or any combination of these. Apply any features that affect the outer geometry of the part, such as fillets on external edges or chamfers on external corners, before shelling. Features that affect external geometry should generally come before Shell in the timeline. Features that you want to add to the inside of the shelled part — such as internal bosses, ribs or mounting lugs — should come after Shell. The one important exception to this rule is that if you plan to add fillets to internal edges after shelling, those fillets need to fit within the wall thickness you have specified. A fillet radius larger than the wall thickness will fail or produce unexpected geometry. If you anticipate needing internal fillets, either increase the wall thickness to accommodate them or apply the fillets before shelling on the solid body where the geometry is simpler. Step 2 — Open Shell Go to Solid → Shell to open the Shell dialog. The dialog shows two main inputs — the faces to remove and the wall thickness — along with an option to apply different thicknesses to specific faces if needed. Step 3 — Select the Faces to Remove Click on one or more faces of your solid body that you want Shell to remove entirely. These become the open faces of the resulting hollow body — the openings through which you access the interior. For a simple box with an open top, click the top face. For a cylindrical cup, click the top circular face. For a two-part enclosure where both halves will be open to mate together, you might select both the top and bottom faces. You can select multiple faces to remove by holding Shif