Mellanox ConnectX-3 metal brackets (WHL #42F2)

No real content this week, just a quick PSA that metal brackets for the ConnectX-3 MCX311A-XCAT 10GbE cards are now available from Chinese sources at very reasonable prices.
The former 3D printed bracket(s) worked fine for more than three years, but always stood out and also required a longer screw due to the material thickness. Finally someone is selling these as metal parts – I don’t think they are original ones as they could be deburred a bit better, but as long as they fit, it’ll do. Available on eBay from multiple sellers already, mine was 4.39 USD including shipping and local 19% VAT.

There’s one caveat: Maybe I only own strange cards that use M3 or UNC 6-32 screw holes and there’s actually a standard on those that suggests another threading – don’t know. But I really expected one of those screw types would fit this bracket. They don’t.

Instead, it’s (most likely) a UNC 4-40 thread. That’s the one that is sometimes used on VGA and RS232/485 D-Sub connectors. A M2.5 screw pushes through the hole easily, and of course UNC #6 and M3 are physically too large to fit, hence the frustration when one tests both types and both do not fit. After fiddling around way longer than I should, I bought a couple more imperial thread cutters so that I can be absolutely sure next time. Furthermore, I just used the M3 cutter to make it M3, there’s enough material around the thread to do that, plus the bracket really doesn’t experience any mechanical stress that one needs to worry about. M3 tap hole diameter is 2.5mm, while UNC #4 tap diameter is 2.3mm with a major diameter of 2.8mm.

It’s a metric bracket now – after all, it’s 10 GbE, not 12.7 GbE, is it…


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