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[Kirk Jarvis]

Hi!

 Designing a lightweight enclosure for a small UAV component, using 4 mm thick anodized aluminum sheets. For the assembly, I need to fasten this plate to a 3D-printed ABS bracket underneath, which acts as a support and needs to be removable. The bracket is tapped, and I’m trying to decide what screw size to use for the through-hole in the aluminum that allows solid clamping without too much play or risk of deforming the hole over repeated assemblies.

Would you size the hole just clearance for an M4, or would M3.5 make more sense considering the wall thickness and material combo? This will likely be assembled/disassembled a dozen times during maintenance.

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[Edward90]

I’d use M4, especially. An M4 screw gives you a bit more strength and better load distribution during clamping, which helps prevent fretting or hole deformation over repeated cycles. You’ll want a standard clearance hole—around 4.3 mm—for the aluminum plate. Since ABS is relatively soft compared to aluminum, the extra thread engagement from the M4 will actually help avoid stripping the tapped holes over time. Plus, you’ve got decent material thickness in the plate to back it up.

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[Kirk Jarvis]

Would an M3.5 be a safer bet for weight savings?

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[eric79]

Maybe if you were really pressed for grams, but in UAV work, reliability usually wins over a few grams. M3.5 screws are much also less common, which could complicate sourcing. M4 is a solid, standard choice with good longevity, and easier to find replacements if needed.

If removability is a key factor, then I’d design to insert nuts or brass inserts into the pillars. The slight extra weight will be compensated by much better re-use characteristics.

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