My mobo has a built-in backplate for socket and cooler and my new AIO screws don't fit.

[Phazoner]

First of all, images of the stock backplate and cooler:

I bought a Silverstone Tundra TD03-SLIM but the screws are too thick. In my eye I really cannot appreciate a size difference between stock cooler screws and the AIO ones, so I think the difference in thickness should be a milimeter as much. How can I solve this situation? For more signs, I installed a Corsair H75 before and it fit perfectly in the stock backplate, but the radiator and fan combo was too thick for my Mini-ITX so I had to go to a thinner one. But I can't see its screws size anywhere.

In this picture you can see the AIO pump installed so you can see how are the screws:

Using the AIO backplate there are big screws from the back which go through that black plastic pieces and finally to the screw with a spring.

 

[Phazoner]

To anyone having this same problem, I bought 2.5mm nuts and screws and worked like a charm. Seems like my AIO screws were 3.5mm, not 3mm, so maybe 3mm would have been a better fit, but anyway the AIO isn't moving. It's tight and freezing so happy ending.

The screws are classified with an "M" so this screws can be found on eBay and other chinese pages as "2.5M screws". This material, even springs, are often classified as 3D printer components, so you can search that way.