BT3 screws? What are they and can I source these anywhere else?

Bambu Lab H2D
1

I am starting an exhaust port project for my H2D and I see I need BT3-20 screws to attach to the back of the machine. I am unfamiliar with this thread call out.
They look to be metric screws (3mm by 20mm) but with a very course thread. Can anyone enlighten me on why these are not just normal M3 machine screws (.5mm pitch I think). are these the same thread and pitch as a 3mm wood screw, just with a flat end and no taper on the point?

Also, I see you can buy them from Bambu, but is there somewhere else I can source these that I don’t have to pay $7 in shipping for a $1 bag of screws?

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As you said it’s metric, an M3 x 20mm machine screw should work. The cap might not match but if you’re just looking to save a couple bucks it should get the job done.

My research leads me to being that the BT is a type 25 screw, which is specifically designed for self tapping threads in plastic. The ridges might be a bit sharper on a normal machine screw but it should still fit I would think

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So I guess that means the mounting holes in the back of the machine are just plastic holes that are to be tapped? that feels dicey for mounting permanent hardware pieces.

I guess if I decide to use machine screws (which I have plenty) I should run a tap in the opening first. but I think it makes sense to use a courser thread like the ones they recommend if I want good bite in a plastic hole.

Guess I will have to buy a roll of filament too to make it worthwhile on the shipping because I can’t seem to find these listed anywhere else.

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No, the thread pitch is VERY different. More than 2x. They look a lot more like a wood screw with most of the pointed tip truncated. Other than being a nominal 3 mm in diameter, they have nothing to do with any metric machine screw.

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Yes BT are self tapping, you can get them on aliexpress or amazon.

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Thats what it looked like to me. I bet a 3MM wood screw with the tip ground down would be a better substitute.

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Typically screws going into plastics are “thread-forming” type, Plastite style, triangular lobed so they roll their own thread (versus “self-tapping” screws).

Usually I’d order from McMaster when I need these, since they’re not commonly available at most local hardware vendors.

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so bambu gave us anything we need to add an exhaust system, except these 4 screws?

edit: my bad, they are in the bag with the clamp…

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I finally found the “generic” term for these screws! Wanted to post it so others can independently source these as well.

1st of all:
BT = blind taper (I’m pretty sure)
3 = size (mm)
SHCS = socket head cap screw

What you’re looking for is “thread rolling screws”
If you type that into Amazon you will see the thread type that the BT3 screws have.
I have yet to find an assortment of these or a 1:1 replacement (SHCS thread rolling), but it’s a step in the right direction.

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