Designing CNC-Threaded Holes for Orthopedic Instruments: How to Prevent Thread Stripping

Created on 10.07

For mechanical engineers, design engineers, and procurement managers in orthopedic device R&D (e.g., bone screws, surgical forceps, implantable tool holders), thread stripping in CNC-machined holes is a critical risk. It leads to part failure during surgery, costly rework, and delayed compliance with medical regulations—all while slowing down new product launches. The good news? Most thread stripping issues are avoidable with smart design choices. Below are 4 key tips to keep your orthopedic CNC-threaded holes strong, plus how Marigold Rapid (www.marigold-rapid.com.cn) supports reliable production.​

1. Match Thread Size, Pitch, and Material Strength​

Orthopedic instruments often use high-strength materials (titanium alloy Ti-6Al-4V, stainless steel 316L) to withstand surgical stress—but mismatched threads break easily. For example:​

Using a fine-pitch thread (e.g., M4×0.5) on a thin titanium bracket can strip under torque, as the thread depth is too shallow.

Fix: Pair materials with compatible threads: Use coarse-pitch threads (e.g., M4×0.7) for thin titanium parts, and fine-pitch for thicker stainless steel components (to reduce weight without losing strength).

2. Avoid Threads Too Close to Part Edges​

Threads near part edges have less material support, making them prone to stripping. For a surgical drill guide with a threaded mounting hole:​

If the hole is less than 1.5× the thread diameter from the edge (e.g., an M5 hole <7.5mm from the edge), the material around the thread will deform under torque.

Fix: Keep threaded holes at least 1.5× the thread diameter away from edges. For tight designs, add a small reinforcement boss around the hole.

3. Design Proper Hole Depth (Don’t Skimp on Engagement)​

Insufficient thread engagement (the length of the screw that connects to the hole) is a top cause of stripping. For orthopedic implants like bone screw receivers:​

Less than 2× the thread diameter of engagement (e.g., an M6 hole with <12mm of thread) means the screw can’t hold torque, leading to stripping.

Fix: Design threaded holes with 2.5–3× the thread diameter of engagement (e.g., 15–18mm for M6 threads) to ensure strength.

4. Add Thread Surface Treatment (Reduce Wear)​

Friction during screw installation wears down threads, causing stripping over time—especially for reusable orthopedic tools.​

Fix: Specify medical-grade surface treatments: For titanium parts, use anodizing to harden threads; for stainless steel, use passivation or nitride coating. These treatments boost thread durability without compromising biocompatibility.

How Marigold Rapid Prevents Thread Stripping in Orthopedic CNC Parts​

At Marigold Rapid, we specialize in orthopedic instrument CNC machining—so we catch thread design flaws before they cause issues. As a one-stop full-process integrated manufacturer, our DFM (Design for Manufacturability) team reviews your threaded hole designs for free, flagging mismatched materials, insufficient engagement, or edge proximity.​

Our fast response means you get feedback in 24 hours—no delays to your orthopedic R&D timeline. Backed by SGS certification (ISO9001 and 13485), our CNC machining uses precision thread-milling tools (instead of tapping) for cleaner, stronger threads—even for small-batch prototype runs. Whether you’re designing bone screw holes or surgical tool mounts, we flexibly adapt to your material and strength needs—zero stripping, zero rework.​

For orthopedic device teams tired of thread-related failures, Marigold Rapid is your reliable partner. Contact us today to review your CNC-threaded hole designs!