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I was using a 2.5 mm hex bit to open and close the extruder.

The 2.5 mm bit is too small and stripped the screw.

The distance on the e-drawing shows that hole to be 2.893 mm or 0.114 inches.

I tried 3 mm and it's definitely too large. The closest size seems to be 7/64 inch.

Does anyone know what the exact hex bit/allen key size is?

Where can the 1/4" or 1/8" type bit be purchased?

[img]http://i.imgur.com/g0iXMdH.jpg[/img]

I got a set of many many bits from a supermarket for a few euro. Yes, 7/64" should be right.

I've just checked my machine, and its a good fit on a 7/64 allen key. I find it helps having a decent quality set, the fit is always better.

I found a bit set with the 7/64 hex/allen bit. The keywords are "33 bit security".

[img]http://i.imgur.com/1FZxQ5E.jpg[/img]

eBay ($5.25)

Harbor Freight ($5.99)

You do not need necessarily the security bits with the holes. But it should work.