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This is a follow on from my previous question, Will standard M5 T-slot nuts fit these different 2020 aluminium extrusions?

The extrusion has this profile:

2020 Aluminium Extrusion BKK#1

and here is a more in-focus photo, of four, in a 2 x 2 configuration:

2020 Aluminium Extrusion BKK#2

The gap, between the bottom of the flange and the top of the circle, is about 4.4 mm high. The M5 hexagonal nuts are 3.85 mm thick, and 7.85 mm wide.

I have been using these 2020 extrusions with regular M5 hexagonal nuts (and M5 bolts, obviously).

However, I have recently found a need to use M3 bolts as well (to secure PCB mounted mechanical switches and endstop holders to the extrusion, for a 3D printer, see Complete list of fasteners for the Sintron Kossel).

The width of the slot is 5.4 mm and regular hexagonal M3 nuts are also around the same width (5.38 mm), and hence slip out of the slot. I guess that I could use a wider washer to hold the nut in place, but does anyone know of a "fat" M3 nut that is available, preferably one that is the same size as an M5 nut, but with a smaller M3 bore?

The problem has arisen because I should be using "European" 2020 aluminium, which takes T-nuts, and those come in a range of bores (M3-M6). However, I have been unable to obtain any, in Bangkok.

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Another option would be to make your own t-nut.

If you have a mill/CNC, here are some instructions to Make a T-Nut

If you don't have access to a mill, you could make a pretty good one out of some 4mm x 5mm bar stock and tap your own holes. All you would need is a drill press and an M3 Tap. The nut may not be as rigid as a t-nut that precisely matches you channel and you can't put as much torque on 4mm of bar stock aluminum as you could on a steel t-nut; but, for most application it would probably be sufficient.

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For the M3 t-nuts, could you use this printed solution. If you are just attaching a PCB, you wouldn't need that much strength.

Another excuse to use your 3D printer. ;)

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The solution would appear to be to use flanged hexagonal nuts1:

Dimensions of flanged hexagonal nut

The height, or thickness, m, of the flanged M3 nut is slightly less than that of an M5 nut and the width, dc, is comparable to that of an M5 nut.


1 However, whilst they fit in the slot, being able to tighten them is another matter altogether, and they will just spin around, as they have no grip on the sides of the slot...

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