How to Choose Screws for Plastic Materials Without Cracking or Stripping

Thread-Forming vs. Thread-Cutting Screws

When it comes to fastening plastic, most screws fall into two categories:

Thread-Forming Screws

• These screws displace the plastic as they enter, creating threads without cutting it.

• Ideal for softer plastics like PP (polypropylene) or PE (polyethylene).

• They offer strong grip but can generate more stress if the plastic is brittle.

Thread-Cutting Screws

• These screws have a cutting edge that removes plastic to form a thread path.

• Better suited for harder plastics such as ABS or polycarbonate.

• They reduce stress but may leave looser threads if over-tightened.

🔍 Tip: If unsure, test both types on scrap plastic. The one that inserts smoothly without cracking or wobbling is your best choice.

Always Pre-Drill Pilot Holes

Plastic behaves differently from wood—it lacks fibers to resist splitting. That’s why pilot holes are essential.

What to Know:

• Use a drill bit that's 70–80% of the screw’s minor diameter.

• Avoid tight fits. Plastic expands and contracts more than metal, so allow some breathing room.

⚠️ Skipping pilot holes is one of the leading causes of cracks when driving screws into plastic.

Mind the Head: Flat, Pan, or Round?

The shape of the screw head affects load distribution on the surface.

• Flat heads: sit flush, ideal when the screw needs to be hidden or countersunk.

• Pan and round heads: better for softer plastics, spreading force over a wider area.

• Truss heads: low-profile, wide-bearing, excellent for thin-walled plastic.

Choose the head based on how much pressure your material can take and how visible the screw will be.

Consider Using Inserts for Reusability

If your application requires repeated disassembly, metal threads in soft plastic will quickly wear out. That’s where inserts come in:

Types of Inserts:

• Heat-set inserts: embedded using a soldering iron or heated press.

• Ultrasonic inserts: vibrated into place, best for industrial production.

• Press-fit inserts: manually inserted, require precise hole sizing.

Inserts can extend the lifespan of plastic components significantly—especially in products like laptops, control panels, or modular enclosures.

Avoid Over-Tightening

Plastic doesn't "push back" the way wood or metal does. When you feel resistance, stop turning.

✅ Use torque-limiting tools when available.
✅ A snug fit is enough. Going further increases risk of stress cracks.

Summary: What to Keep in Mind

• ✅ Use thread-forming screws for softer plastics.

• ✅ Opt for thread-cutting screws for harder plastics.

• ✅ Always pre-drill pilot holes to avoid cracking.

• ✅ Choose screw heads based on surface load needs.

• ✅ For reusability, use inserts instead of direct threading.

• ✅ Avoid over-tightening—torque matters!

Need Custom Fasteners for Plastic? Let Fasto Help.

At Fasto, we design and supply fasteners with real-world performance in mind—including screws and inserts tailored for plastic materials.

Whether you're developing consumer electronics, custom enclosures, or structural plastic components, our team is here to assist you with:

• 🔧 Custom specifications

• 📦 Scalable supply

• 🌍 Global shipping

Even if the product isn’t listed on our website yet, feel free to reach out. We support custom sourcing and manufacturing for plastic fasteners—because every design deserves the right hold.

📧 info@fasto.cn
🌐 Explore our catalog or request samples today!