ASUS ROG CROSSHAIR VI - mobo
EVGA 1080 Ti FTW3 x2 - GPUs

Here is the chart that you can use to figure out what size to use depending what slots you use on the board.
 

I am surprised this question still gets adked when there is a HB Sli Bridge thread woth this exact question answered so many times that it is ridiculous..

Also, at least on my phone, if I Google SLI bridge size needed for my exact motherboard this thread is the first response.

Anyway, I went and physically measured and from inside edge to inside edge between the two appropriate slots it is exactly 2 inches - which is 50.8mm which isn't the exact answer I was looking for.

The entire thread about the sli bridges, in the "other evga hardware: sli bridges" and such forum:

1:) https://forums.evga.com/E...0811.aspx?high=Hb+sli+

2:) https://forums.evga.com/N...7401.aspx?high=Hb+sli+

3:) https://forums.evga.com/W...5617.aspx?high=Hb+sli+ < same spacing as your board, same bridge

4:) https://forums.evga.com/W...0696.aspx?high=Hb+sli+ <same, same

5:) https://forums.evga.com/S...6162.aspx?high=Hb+sli+

6:) https://forums.evga.com/W...5617.aspx?high=Hb+sli+ same same

All I typed was HB Sli in to the forum search and returned 2 full pages of the results. You may consider people rude for being honest, but it's easy to find results since all of the boards are set to a standard. Nvidia and evga both provide easy to follow pictures as well, but no one uses the pictures.

The above links are just some examples. I thought 6 was excessive, but it gets the point across without being "rude".

Also, dont take offense.. you're not the first or last that will ask without seeing all of the other answers. This question has been answered constsntly for years. All sli bridges were the same across the years, but since the lighted bridges were provided, people started asking more and more, even after the answers were provided.