1. Identify Your Joint Type: This guide applies to 'single shear' joints, where two pieces of wood are fastened side-by-side and the force is trying to slide them apart.
2. Select Screw Size: Choose the size of the screw you plan to use from the dropdown list.
3. Select Screw Material: Choose between standard zinc-plated steel and stainless steel.
4. View Estimated Strength: The calculator will display the approximate load in pounds that a single screw of that type can resist before shearing.

• Shear Strength: The maximum stress a material can withstand before failing in a shear-like manner. In fasteners, it's the force required to slice the screw's body.
• Single Shear: A joint where a fastener passes through two members, and the load is applied in one plane. This is the most common type of shear joint in woodworking.
• Double Shear: A joint where a fastener passes through three members (e.g., a central piece between two outer plates). This type of joint is significantly stronger.
• Tensile Strength: The ability of a fastener to resist being pulled apart. Also known as withdrawal strength.
• Yield Strength: The point at which a material begins to deform permanently under stress.

"In woodworking, the wood itself is almost always the weakest link, not the screw. A properly sized screw will rarely shear off. Instead, the wood fibers around the screw will crush and fail first. That's why using more, smaller screws is often better than one massive screw—it distributes the load over a larger area of wood." - Structural Engineer

"Don't just think about the screw. Think about the entire joint. The distance of the screw from the edge of the board is critical. A screw placed too close to the edge doesn't give the wood enough material to resist the shear force, and the wood will split out long before the screw fails."

Example 1: Building a Deck Ledger Board
A ledger board attached to a house is a classic shear joint. The weight of the deck is trying to 'slice' the lag screws. Using multiple, large-diameter lag screws (e.g., 1/2" or 5/8") is required by building codes to safely handle these massive shear loads.

Example 2: Assembling a Cabinet Face Frame
When you join the rails and stiles of a face frame with pocket screws, the joint is primarily under shear stress. While the loads are small, using a quality pocket screw ensures the joint won't slip or misalign under pressure.

• Over-relying on a Single Fastener: Good design never relies on one screw for a critical connection. Use multiple fasteners to distribute the load and provide redundancy.
• Using the Wrong Type of Fastener: Using brittle drywall screws for a structural joint that is under shear stress is a common and dangerous mistake.
• Ignoring Wood Failure: Focusing only on the screw's strength and forgetting that the wood around it can crush, split, or tear out.
• Not Considering Combined Forces: In the real world, joints are often under a combination of shear and withdrawal (tensile) forces. This must be considered in the design.

• Structural Joints: Understanding the forces at play in load-bearing applications like deck building or framing.
• Hardware Selection: Making informed choices about screw size and material for a given application.
• Furniture Design: Designing stronger joints by understanding how fasteners resist different types of stress.
• Educational Tool: Providing a visual and interactive way to learn about mechanical engineering principles in woodworking.