---
title: "Which screw should I use in plastic?"
description: "A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once. The ranked options, the technique that chan"
url: https://atoneplace.net/which/screw-plastic/
site: "At One Place"
---

# Which screw should I use in plastic?

**Which screw should I use in plastic?: A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once.**

Plastics fail at fixings in two ways: brittle materials such as polystyrene and acrylic crack from the hoop stress a thread creates, and ductile ones such as polypropylene creep, so a joint tightened today is loose in six months. Thread-forming screws for plastics are designed around both, with a wide thread angle to reduce hoop stress and a large flank area to spread load. The other rule is torque: plastic bosses strip at a fraction of the torque a metal thread takes, so a power driver on its highest clutch setting will destroy the boss before you feel anything. Anything intended to be opened more than a handful of times should have a metal insert rather than a thread cut in plastic.

## The options, ranked

*Ranked best-first for the stated job. The third column is why the others exist.*

| Option | Good at | Bad at |
| --- | --- | --- |
| Thread-forming plastic screw | A wide, shallow, single-lead thread displaces material rather than cutting it, so it does not crack the boss. | Specific to plastics and not stocked everywhere. |
| Heat-set threaded insert | Melts into a moulded boss and gives a metal thread that can be assembled repeatedly — the standard in 3D-printed parts. | Needs a soldering iron and the right hole size. |
| Machine screw and captive nut | Strongest and fully demountable. | Needs access to both sides or a designed-in nut trap. |
| Standard woodscrew | Works once in soft plastics. | Its sharp, deep thread wedges brittle plastics apart, and every reassembly strips the hole further. |

## Technique that changes the outcome

1. Use the boss and pilot dimensions the screw maker publishes; they are specific and they matter
2. Set the driver clutch low and finish by hand
3. For repeated assembly, install a heat-set insert with a temperature-controlled iron
4. Support brittle plastic around the fixing so the hoop stress has somewhere to go

## What goes wrong

- Overtightening, which strips the boss in an instant
- Woodscrews in brittle plastics
- Reusing a stripped hole; move to an insert or a machine screw

> Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.

## Other screw questions

| For | Use |
| --- | --- |
| Wood | A pilot hole matching the screw's core diameter in the lower piece and a clearance hole in the upper one — that is what makes a joint tight. |
| Decking | Stainless steel — 304 inland, 316 near the coast — or a screw specifically rated for modern treated timber, which eats ordinary zinc plating. |
| Masonry | A concrete screw into a precisely sized hole, or a plug and screw — and hollow block needs a different anchor entirely. |
| Plasterboard | Coarse-thread bugle-head drywall screws into timber studs, fine-thread into metal studs — and never use them for anything structural. |
| MDF | A straight-shank MDF screw with a parallel thread, always into a pilot hole — the edge splits without one. |
| Sheet metal | A self-drilling (Tek) screw with a drill point matched to the material thickness, or a self-tapping screw into a correctly sized pilot hole. |
| Chipboard | A twin-thread chipboard screw with an unthreaded shank under the head, so it pulls the joint together instead of bursting the board. |
| Roofing sheets | A hex-head screw with a bonded EPDM washer, driven until the washer just spreads — no further. |
| Brass hardware | Cut the thread with a steel screw of the same size first, wax the brass one, and use a driver that fits the slot exactly. |

## Common questions

### Which screw should I use in plastic?

A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once.

### What should I avoid?

Overtightening, which strips the boss in an instant Woodscrews in brittle plastics Reusing a stripped hole; move to an insert or a machine screw

## Related pages

- [Which screw and pilot hole should I use for wood?](https://atoneplace.net/which/screw-wood/)
- [Which screw should I use for decking?](https://atoneplace.net/which/screw-decking/)
- [Which screw should I use in masonry?](https://atoneplace.net/which/screw-masonry/)
- [Which screw should I use for plasterboard?](https://atoneplace.net/which/screw-plasterboard/)
- [Which screw should I use in MDF?](https://atoneplace.net/which/screw-mdf/)
- [Which screw should I use for sheet metal?](https://atoneplace.net/which/screw-sheet-metal/)
- [Which screw should I use in chipboard?](https://atoneplace.net/which/screw-chipboard/)
- [Which screw should I use for roofing sheets?](https://atoneplace.net/which/screw-roofing/)
- [How do I drive brass screws without snapping them?](https://atoneplace.net/which/screw-brass-hardware/)
- [Which glue works on plastic?](https://atoneplace.net/which/glue-plastic/)
- [Which drill bit should I use for plastic?](https://atoneplace.net/which/drill-bit-plastic/)
- [Which sandpaper grit for plastic?](https://atoneplace.net/which/sandpaper-plastic/)
- [Which paint sticks to plastic?](https://atoneplace.net/which/paint-plastic/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)