What are the best (basically strongest) plastic screws made of?

[Chris Green]

I need some M4 x 12mm countersunk plastic screws. The obvious easily
obtained material is nylon but I see that some other plastics are also
available - e.g. clear acrylic.

I'm not expecting metal strength but it would be good to know which
(reasonably priced) plastic is going to be stronger. I'm aming to use
the screws through a sheet of closed-cell plastic to pull things
'into' the plastic (rather like upholstery buttons).

[Theo]

Post by Chris Green
I need some M4 x 12mm countersunk plastic screws. The obvious easily
obtained material is nylon but I see that some other plastics are also
available - e.g. clear acrylic.
I'm not expecting metal strength but it would be good to know which
(reasonably priced) plastic is going to be stronger. I'm aming to use
the screws through a sheet of closed-cell plastic to pull things
'into' the plastic (rather like upholstery buttons).

Acrylic is very brittle and propagates cracks easily - not what you want for
a screw.

Nylon (polyamide/PA) is pretty good as a mechanical element. There's also
various forms of fibre-reinforced nylon (GFR PA) which are stronger but not
sure you can make a sensible fibre lay-up for a small screw.

Don't overtighten, as I think that's a common cause of nylon failure - the
screw head shears off.

Theo

[The Natural Philosopher]

Post by Theo

Post by Chris Green
I need some M4 x 12mm countersunk plastic screws. The obvious easily
obtained material is nylon but I see that some other plastics are also
available - e.g. clear acrylic.
I'm not expecting metal strength but it would be good to know which
(reasonably priced) plastic is going to be stronger. I'm aming to use
the screws through a sheet of closed-cell plastic to pull things
'into' the plastic (rather like upholstery buttons).

Acrylic is very brittle and propagates cracks easily - not what you want for
a screw.
Nylon (polyamide/PA) is pretty good as a mechanical element. There's also
various forms of fibre-reinforced nylon (GFR PA) which are stronger but not
sure you can make a sensible fibre lay-up for a small screw.
Don't overtighten, as I think that's a common cause of nylon failure - the
screw head shears off.

Pretty much all there. I found acrylic as will, but if it is a low
grade plastic screw nylon seems to be most used

In the model aircraft arena, the ability of nylon bolts to shear in a
crash is desirable

I actually found that at least with cross heads, the screwdriver could
not exert enough torque to shear them - the heads just mashed first.

Post by Theo
Theo

[Clive Arthur]

Post by Chris Green
I need some M4 x 12mm countersunk plastic screws. The obvious easily
obtained material is nylon but I see that some other plastics are also
available - e.g. clear acrylic.
I'm not expecting metal strength but it would be good to know which
(reasonably priced) plastic is going to be stronger. I'm aming to use
the screws through a sheet of closed-cell plastic to pull things
'into' the plastic (rather like upholstery buttons).

I sometimes specify PEEK fasteners, mainly because of temperature.
They're pretty strong, though unreasonably priced.

https://highperformancepolymer.co.uk/products/countersunk-peek-flat-head-screws?variant=44169076539690

[GB]

Post by Clive Arthur

I need some M4 x 12mm countersunk plastic screws.  The obvious easily
obtained material is nylon but I see that some other plastics are also
available - e.g. clear acrylic.
I'm not expecting metal strength but it would be good to know which
(reasonably priced) plastic is going to be stronger. I'm aming to use
the screws through a sheet of closed-cell plastic to pull things
'into' the plastic (rather like upholstery buttons).

I sometimes specify PEEK fasteners, mainly because of temperature.
They're pretty strong, though unreasonably priced.
https://highperformancepolymer.co.uk/products/countersunk-peek-flat-head-screws?variant=44169076539690

The good news is that the patent will expire pretty soon, assuming this
is the key one:

https://patents.google.com/patent/US8236919B2/en

[Clive Arthur]

<snip>

Post by GB

Post by Clive Arthur
I sometimes specify PEEK fasteners, mainly because of temperature.
They're pretty strong, though unreasonably priced.
https://highperformancepolymer.co.uk/products/countersunk-peek-flat-head-screws?variant=44169076539690

The good news is that the patent will expire pretty soon, assuming this
https://patents.google.com/patent/US8236919B2/en

Interesting. I've just now received spam email advertising a frying pan
with PEEK non-stick coating. Fifty-seven quid, so not outrageous.

[Theo]

Post by Clive Arthur
<snip>

Post by GB

Post by Clive Arthur
I sometimes specify PEEK fasteners, mainly because of temperature.
They're pretty strong, though unreasonably priced.
https://highperformancepolymer.co.uk/products/countersunk-peek-flat-head-screws?variant=44169076539690

The good news is that the patent will expire pretty soon, assuming this
https://patents.google.com/patent/US8236919B2/en

Interesting. I've just now received spam email advertising a frying pan
with PEEK non-stick coating. Fifty-seven quid, so not outrageous.

I got that spam too. I didn't read it, so I thought PEEK was a brand of
frying pan.

Seems like PEEK is being touted as a replacement for PFAS which have
environmental problems. Also seems to be better at high temperatures,
something PFA/PTFE coated bakeware struggles with.

Theo

[SteveW]

Post by Theo

Post by Clive Arthur
<snip>

Post by GB

Post by Clive Arthur
I sometimes specify PEEK fasteners, mainly because of temperature.
They're pretty strong, though unreasonably priced.
https://highperformancepolymer.co.uk/products/countersunk-peek-flat-head-screws?variant=44169076539690

The good news is that the patent will expire pretty soon, assuming this
https://patents.google.com/patent/US8236919B2/en

Interesting. I've just now received spam email advertising a frying pan
with PEEK non-stick coating. Fifty-seven quid, so not outrageous.

I got that spam too. I didn't read it, so I thought PEEK was a brand of
frying pan.
Seems like PEEK is being touted as a replacement for PFAS which have
environmental problems. Also seems to be better at high temperatures,
something PFA/PTFE coated bakeware struggles with.

It's long been used in industrial valve seats.

[Andy Burns]

Post by Chris Green
I need some M4 x 12mm countersunk plastic screws. The obvious easily
obtained material is nylon

What about Delrin? aka Polyoxymethylene or POM

[Paul]

Post by Andy Burns

I need some M4 x 12mm countersunk plastic screws.  The obvious easily
obtained material is nylon

What about Delrin? aka Polyoxymethylene or POM

https://bbs-industrie.com/materials/plastic/pom/

"not particularly UV resistant"

*******

This is advice from CoPilot.

Q: What is the best material to use to make a uV-resistant screw ?

A: The best materials for making a UV-resistant screw are plastics like
Acrylic (PMMA), Polycarbonate, PTFE, HDPE, Polyetherimide, Polyphenylene Sulfide,
and Polyvinylidene Fluoride. These materials are known for their
excellent UV resistance and are suitable for outdoor applications where
exposure to sunlight is a concern.

For instance, Acrylic and Polycarbonate are both strong and durable,
with Polycarbonate being particularly noted for its impact resistance.

If you’re considering metal screws, stainless steel screws are a
good option as they offer exceptional rust resistance and can
withstand outdoor conditions.

It’s important to choose the right material based on the specific
requirements of your application, such as strength, flexibility,
and environmental resistance.

https://www.mcmaster.com/products/polycarbonate-screws/?s=polycarbonate-screws

Paul

[alan_m]

Post by Paul

Post by Andy Burns

I need some M4 x 12mm countersunk plastic screws.  The obvious easily
obtained material is nylon

What about Delrin? aka Polyoxymethylene or POM

https://bbs-industrie.com/materials/plastic/pom/
"not particularly UV resistant"
*******
This is advice from CoPilot.
Q: What is the best material to use to make a uV-resistant screw ?
A: The best materials for making a UV-resistant screw are plastics like
Acrylic (PMMA), Polycarbonate, PTFE, HDPE, Polyetherimide, Polyphenylene Sulfide,
and Polyvinylidene Fluoride. These materials are known for their
excellent UV resistance and are suitable for outdoor applications where
exposure to sunlight is a concern.
For instance, Acrylic and Polycarbonate are both strong and durable,
with Polycarbonate being particularly noted for its impact resistance.
If you’re considering metal screws, stainless steel screws are a
good option as they offer exceptional rust resistance and can
withstand outdoor conditions.
It’s important to choose the right material based on the specific
requirements of your application, such as strength, flexibility,
and environmental resistance.
https://www.mcmaster.com/products/polycarbonate-screws/?s=polycarbonate-screws

As that article mentions, it depends on the application and also
reliance on the material not being too malleable or brittle. If trying
to hold two pieces together that have a natural tendency to pull apart
you will not want to use a material that may stretch over time or when
fitting, nor when attempting to tighten that last quarter of a turn just
snaps.

It's much like the "plastic" back washers that come with many taps these
days. Great that they will not rust* but I've found when in an awkward
position and trying to tighten them the internal tread can deform and
jump back a tread effectively loosening the nut as you tighten. Once
this has happened once the chances of tightening are zero. I always
throw away the plastic back nuts and purchase the brass* versions.

*
I've encountered brass coloured steel versions that have rusted over 15
years :(

[The Natural Philosopher]

Post by alan_m
It's much like the "plastic" back washers that come with many taps these
days. Great that they will not rust* but I've found when in an awkward
position and trying to tighten them the internal tread can deform and
jump back a tread effectively loosening the nut as you tighten. Once
this has happened once the chances of tightening are zero. I always
throw away the plastic back nuts and purchase the brass* versions.

Yes 100%. I have a wobbly tap with an untightenable cracked plastic nut
that is in such an awkward place it been waiting around 6 years to be
replaced...

[GB]

Post by The Natural Philosopher

Post by alan_m
It's much like the "plastic" back washers that come with many taps
these days. Great that they will not rust* but I've found when in an
awkward position and trying to tighten them the internal tread can
deform and jump back a tread effectively loosening the nut as you
tighten. Once this has happened once the chances of tightening are
zero. I always throw away the plastic back nuts and purchase the
brass* versions.

Yes 100%. I have a wobbly tap with an untightenable cracked plastic nut
that is in such an awkward place it been waiting around 6 years to be
replaced...

Is it wobbly enough to get a squirt of silicone under the flange to bond
it to the sink.

[The Natural Philosopher]

Post by GB

Post by The Natural Philosopher

Post by alan_m
It's much like the "plastic" back washers that come with many taps
these days. Great that they will not rust* but I've found when in an
awkward position and trying to tighten them the internal tread can
deform and jump back a tread effectively loosening the nut as you
tighten. Once this has happened once the chances of tightening are
zero. I always throw away the plastic back nuts and purchase the
brass* versions.

Yes 100%. I have a wobbly tap with an untightenable cracked plastic
nut that is in such an awkward place it been waiting around 6 years to
be replaced...

Is it wobbly enough to get a squirt of silicone under the flange to bond
it to the sink.

BTDTGTTS

It just unscrewed even more

[The Natural Philosopher]

Post by Andy Burns

I need some M4 x 12mm countersunk plastic screws.  The obvious easily
obtained material is nylon

What about Delrin? aka Polyoxymethylene or POM

I could not find anyone making screws out of that.

[Chris Green]

Post by The Natural Philosopher

Post by Andy Burns

I need some M4 x 12mm countersunk plastic screws.  The obvious easily
obtained material is nylon

What about Delrin? aka Polyoxymethylene or POM

I could not find anyone making screws out of that.

Quite! OP here, the basic choice for easily obtained (and not stupidly
expensive) screws seems to be between nylon and acrylic. Having found
a few sites with information I think nylon is almost certainly the way
to go for my application.

[Paul]

Post by Chris Green

Post by The Natural Philosopher

Post by Andy Burns

I need some M4 x 12mm countersunk plastic screws.  The obvious easily
obtained material is nylon

What about Delrin? aka Polyoxymethylene or POM

I could not find anyone making screws out of that.

Quite! OP here, the basic choice for easily obtained (and not stupidly
expensive) screws seems to be between nylon and acrylic. Having found
a few sites with information I think nylon is almost certainly the way
to go for my application.

Is this an outdoor application ?

White nylon seems quite UV sensitive (a problem after one year).
Black nylon is better, but they don't make screws of it (at least 4 to 5 year life).

You may want to review thread design, in case what was tapped into the
steel, is different than how they cut the plastic ones.

https://en.wikipedia.org/wiki/Screw_thread

Paul

[Chris Green]

Post by Paul

Post by Chris Green

Post by The Natural Philosopher

Post by Andy Burns

I need some M4 x 12mm countersunk plastic screws.  The obvious easily
obtained material is nylon

What about Delrin? aka Polyoxymethylene or POM

I could not find anyone making screws out of that.

Quite! OP here, the basic choice for easily obtained (and not stupidly
expensive) screws seems to be between nylon and acrylic. Having found
a few sites with information I think nylon is almost certainly the way
to go for my application.

Is this an outdoor application ?

No, it's inside and hidden under panelling so will be kept in the
dark! :-)