The fan support is 3/4 x 3/4. I ordered two different size brackets from two different companies. One is 3/4 wide and the other is 1 inch wide. I went with the bigger one and used some stainless steel washers to take up the space. I found this easier because it's difficult to get the brackets perfectly parallel. Also, the 1 inch bracket is longer and beefier. The bottom one is one I went with.
https://www.allpartitions.com/urtwoearheav.html
https://www.robertbrooke.com/chrome-...2-x-3-1-2.html I used this one. Picture on bottom