I can confirm 100% that this bracket #MTM003170
Mellanox MTM003170 FRU Tall Bracket for 1-port SFP+ adapter. Fits MNPA19
works perfectly fine with the ConnectX-3 MCX311A-XCAT. As I mentioned on the last page, it is NOT a fully perforated bracket but it fits and the card plugs into a slot properly, etc. Also I can confirm that the screws from the SFF bracket also fit the full size brackets. These are cheaper and in stock. Again from the previous page, this bracket is intended for the ConnectX-2 MNPA19 cards but it works perfect on the ConnectX-3 card just as well. I bought 8 of them directly from Mellanox and they came in this morning and I tested to make sure they fit the ConnectX-3 cards I bought.
These are for the single SFP+ port cards ONLY. They will not work for a dual port card or a card with some other type of port. Also as you can see in this picture, the bracket for the older card has two holes for LED's while the newer card only has a single LED and that single LED does not line up exactly with the hole in the bracket. It is however close enough to the holes that you can still see the activity LED from the back of the machine well enough. In this picture you can see the tiny LED just to the right of the hole in the bracket. Mellanox shows this bracket as in stock, ships the same day and is $4.30 each. On my order of 8 the shipping was another $12....