I have been looking for some kind of permanent fastener to replace the standard M3/20 machine screws, but which:

1. Can be hammered rather than screwed into the core.
2. Can't be pulled back out or removed by unscrewing it.

I'm thinking it might have just a few round/circular threads at the end, rather than one long helical thread.

I'm sure this type of permanent fastener must exist, but I don't know what it's called so haven't been able to find anything that would work as explained above.

Does anybody know what these are called, or know somebody who would know? Has anyone seen or used anything like this before, and where can one buy them?

I know Rubik’s brand Cubes have rivets which sound similar to what you are saying.
I’m not sure they can be hammered though.

Yes I have seen them, I am sure they can be hammered in and are probably used because they are much quicker to put in than screws. Do you know what they are called? If they are rivets, what type of rivets are they?

You could try here to see if they have anything which is suitable.

I think that the hardest thing about force fitting fasteners is the amount of damage which can be done to the material being fastened if the hole does not have a tight tolerance. I have had bad experience using force fit pins into PCBs. Another problem is that you need to ensure that the fastener is pushed in parallel to the axis of the hole - we have to use a special tool.

Thanks I'll take a look.

I'm not too worried about damaging the core as this is made of nylon, which is virtually indestructable, whereas PCBs are made of very brittle plastic. And some kind of simple widget can be made to ensure proper alignment (as well as correct depth to control spring tension), so I'm not worried about that either. Main thing is to reduce assembly time (avoid screwing) and also make sure the fasteners won't come loose. I guess that's exactly what they did with the Rubik's Cube.

I see your point. BTW, PCBs are made from glass reinforced epoxy resin, and they are very durable and strong. But they are prone to edge damage due to de-lamination, especially when pins are force fitted into holes incorrectly..