First, hook the fan clips into the mounting holes of the fan on both sides.

Then hook the fan clips into the notch on the heatsink on both sides simultaneously. 

If the fan still does not sit tightly, you may be able to secure it more tightly by pulling the fan clips tighter (to a further clip position) as some of our fan clips are designed with multiple points that can attach to a heatsink. Here’s an example of what it should look like on the NH-D15: 

NH-D15 G2 load-relief fan clips

The load-relief fan clips on the NH-D15 G2 coolers attach differently than our standard fan clips. Instead of hooking into the fans' outer mounting holes, these clips are positioned between the two mounting holes.