Direct threading into soft materials like aluminum, magnesium, or plastic is a known weak point in mechanical design: the thread wears out, weakens, and sometimes completely fails after several disassembly and assembly cycles. In this guide, we will review the two main solutions to this problem: Helicoil and Keensert, and explain when each is the right choice. 1. The Problem Threaded Inserts Solve When screwing directly into a soft material, each repeated disassembly and assembly wears down the thread a little more. After several threading cycles, the effective thread diameter increases, and the clamping force progressively decreases until the thread completely fails. Common Solution: Adding a Threaded Insert that creates a durable thread within a pre-drilled hole in the base material. How it Works: Instead of the screw threading directly into the soft material, it threads into an insert made of hard metal (usually steel), which is anchored in the base material. The Result: The screw interfaces with a much more durable thread, not the original thread of the soft material. 2. Helicoil: The Solution for Repairing and Preserving Existing Threads A Helicoil is a flexible metal coil with a rhombic cross-section, which threads into a pre-tapped hole in the base material. It effectively restores the original thread size and form. Ideal Use: Repairing worn or damaged threads. Key Advantage: A lightweight and cost-effective solution, also suitable for original design in serial production when the anticipated load is not extreme. When to Use? When there are space constraints — the outer diameter of the Helicoil is very close to the original thread diameter, unlike a Keensert which requires a larger hole. 3. Keensert: The Threaded Anchor for Soft Materials A Keensert is a solid bushing insert that is installed by external threading into a prepared hole in the base material, followed by a locking stake that prevents it from detaching from the hole. Ideal Use: Industrial assemblies with high axial loads and frequent threading cycles, such as disassembly for routine maintenance. Key Advantage: A rigid body and a precise internal thread, which functions as a "standard" thread for the screw that connects to it. When to Use? When the base material is significantly softer than the metal (aluminum, magnesium, plastic), and high resistance to cumulative wear over thousands of cycles is required. 4. Helicoil or Keensert: Quick Comparison Table Criterion Helicoil Keensert Main Purpose Repairing an existing worn thread Original design under high load Lateral and Torsional Load Medium High Space Requirement (Hole Diameter) Small, close to the original thread Larger Installation Complexity Low Higher (including staking) Resistance to Disassembly-Assembly Cycles Good Excellent 5. Keensert Installation Steps: Why It Matters for Selection Drilling a pilot hole: To precise diameter and depth according to the manufacturer's table. Tapping: Creating a thread with a diameter matching the Keensert body. Threading the Keensert: To full depth into the prepared hole. Staking: Tightening "locking wings" at the end of the Keensert to prevent it from retreating from the hole under load. This complexity means that a design based on a Keensert must account for the additional manufacturing steps in advance — it is not an insert suitable for "on-the-spot repair" but for a design that considers it already at the mechanical design stage. 6. Checklist Before Ordering Thread Diameter and Pitch: The required data for the external screw that will connect to the insert. Type and Strength of Base Material: Aluminum, magnesium, or plastic. Available Threading Depth: How much space is available in the assembly for the insert itself. Number of Disassembly-Assembly Cycles: Expected product lifespan, which directly influences the choice between Helicoil and Keensert. Need further consultation? We at A. Zilka Marketing & Engineering are here for you. You can view the full catalog in the Screws category, or contact our sales team for technical advice on matching the right insert for your project.
