HDPE - Coarse or fine threads

[greencat]

I'm building a dog ladder for a boat out of HDPE. It's a long story and I will post pictures if it works.

Question
I'm joining 2 pieces of HDPE. I was planning on using Stainless Steel machine screws with a 10-24 thread. Should I use a coarse thread? What is the rule of thumb - the more dense the finer the thread?

Thanks

[Tequila]

I found a few sites that suggest coarse wood screws. If you're going with machine screws, you might want to try using t-nuts to add some holding strength.

[LCHIEN]

I'm building a dog ladder for a boat out of HDPE. It's a long story and I will post pictures if it works.

Question
I'm joining 2 pieces of HDPE. I was planning on using Stainless Steel machine screws with a 10-24 thread. Should I use a coarse thread? What is the rule of thumb - the more dense the finer the thread?

Thanks

10-24 is the coarse thread (24 threads per inch)
10-32 is the fine thread (32 threads per inch).

More threads = finer pitch.

I don't think machine screw threads will hold well in that plastic.
You would probably do better with Sheet metal screws or even wood screws.

Not really sure how you are using these. - e.g fastening items to solid HDPE? or
fastening sheets of HDPE to solid HDPE? or what?

[vaking]

As a general rule - coarse thread is stronger. This is especially true for soft material (cast iron and copper are soft materials, HDPE is even softer). Fine thread is superior only on thin wall constructions like tubing.
Here is the link if you want:
http://www.efunda.com/designstandard...ws/screwun.cfm
Stay away from sheet metal screws - they have fine threads. I would rather choose drywall screws except that I don't know if there are rust resistant drywall screws.