Suitable for plastic parts with relatively thick walls and low stress requirements (e.g., toy casings, small household appliance housings). Prioritize "engagement reinforcement" methods:
Cut a small piece of rubber gasket, silicone sheet, or 青稞 paper (thickness: 0.1-0.3mm), punch a hole in the center, slide it over the screw, then align and tighten the screw into the threaded hole.
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Principle: The gasket fills the gaps caused by thread wear. Meanwhile, the high friction of rubber/silicone prevents the screw from slipping without additional damage to the plastic threads.
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Note: The diameter of the gasket should be smaller than the screw head to avoid exposure that affects appearance or assembly.
If the screw only needs to be "fixed without disassembly," apply a thin layer of instant adhesive (e.g., 502 glue) or low-strength anaerobic adhesive (e.g., Loctite 243) to the screw threads. Quickly insert the screw into the threaded hole and tighten it, holding it in place for 10-20 seconds to set.
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Principle: Once cured, the adhesive fills thread gaps and enhances engagement strength. Low-strength adhesive can be broken by forcefully twisting the screw with a screwdriver if disassembly is needed later (avoid high-strength adhesive, as it may cause the plastic part to crack).
Suitable for plastic parts with a certain wall thickness (≥3mm) where thread functionality needs to be restored (e.g., equipment panels, plastic brackets):
Use a drill bit 1-2 sizes larger than the original threaded hole (e.g., replace an M3 drill bit with an M4 bit for an original M3 hole) and slowly drill through the stripped hole (reduce drill speed to prevent plastic melting).
Replace the screw with the corresponding size (e.g., an M4 screw). Tighten with moderate force (torque for plastic parts is usually ≤5N・m, controllable with a torque screwdriver). The new screw’s threads will "repress the plastic" to form a new engagement.
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Note: Before enlarging the hole, confirm there are no other components (e.g., circuits, gears) on the back of the plastic part to avoid damaging internal structures when the drill bit penetrates through.
Select epoxy AB glue (e.g., Deli AB glue) or plastic repair compound (e.g., Devcon 10110), mix it in the specified ratio, and fill the stripped threaded hole—ensure the filler fully fills thread gaps. Let it cure undisturbed (follow product instructions, usually 2-4 hours).
After curing, redrill the hole with the original-size drill bit (use low speed and blow away plastic shavings while drilling), then reinsert the original screw.
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Advantage: The repaired thread strength is close to the original, making it suitable for medium-stress scenarios (e.g., fixing plastic clips).
Suitable for plastic parts with thin walls or long-term stress requirements (e.g., mechanical structural parts, load-bearing brackets). "External reinforcement" is required to restore functionality:
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Tools: Select a plastic-specific metal thread insert (also called an "inlay," usually made of brass, with an inner diameter matching the original screw) and a heat gun or soldering iron.
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Procedure:
① Heat the metal thread insert with a heat gun (temperature: approx. 150-200℃; avoid overheating to prevent plastic melting);
② Quickly press the heated insert into the stripped threaded hole (gentle rotation can assist insertion);
③ After cooling, directly screw the original-size screw into the insert.
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Advantage: Metal thread inserts withstand higher torque and tension, and the repaired joint has a much longer service life than the original plastic thread. Suitable for scenarios requiring frequent disassembly or stress (e.g., fixing instrument housings).
If the area around the threaded hole is severely damaged, cut a small piece of plastic sheet (same material as the part) or thin metal sheet. Use a plastic welding gun (or AB glue) to attach it to the outside of the threaded hole as a "patch," ensuring the patch adheres firmly to the plastic part.
After the patch cures, redrill and tap the hole at the original threaded hole position (if the plastic is soft, the screw can self-tap directly without tapping), then insert the screw.
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Note: Metal patches must be sanded smooth to avoid scratching other components; for plastic parts with high appearance requirements, a plastic patch of the same color is recommended.
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Do not force-tighten the screw: Continuing to apply force after thread stripping will further wear the threads and may even crack the plastic part.
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Avoid direct contact between high-temperature tools and plastic: Control the temperature of tools like soldering irons or heat guns, and avoid prolonged contact to prevent plastic melting or deformation.
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Do not randomly fill with "hard materials": Materials like steel wire or toothpicks may provide temporary fixation but easily break under stress, causing additional damage to the plastic part.
If thread stripping recurs after repair, the plastic part itself may be aged (e.g., embrittlement due to long-term exposure to high temperatures). It is recommended to replace the plastic part with a new one to solve the problem at its root.
