Reddit mentions of Noctua NA-SAV2 chromax.black, Silicone Anti-Vibration Fan Mount Set (20-pack, Black)

Just ran into that same issue. Those screws work if you're going through the case into the fan (like on the exhaust) but obviously don't really cut it going the other way. My case came with some longer screws kinda like this that I used. You could probably also use the rubber thingies like this

edit: I'm assuming you are trying to go through the front of the fan to mount it to the case on the other side of the fan, yes?

Are you removing a case side and letting an external fan sitting on the floor blow air into the case? If so that's okay, but maybe make your components dusty faster.

About better case fans, please keep in mind improving case fans can only do so much to increase airflow to GPU, so don't get your expectations too high about how much cooler/quieter your GPU will become. If you really want a quiet GPU, you should have gotten a GPU designed with big heatsink and good fans, then it could be silent or almost silent by itself.

If you have PWM 4-pin fan headers, I think Corsair ML120 and ML140 push a bit more air than Noctua equivalent for the same noise level, but if you don't have PWM 4-pin fan headers, the Corsair ML's can make a lot of noise because of their magnetic bearing not working properly. Also ML's seems to be quite bad pushing air directly downwards and make a lot of noise positioned that way for me, in case you have an airflow setup that requires intake from the top or exhaust into the bottom of your case.

ML's can be bought in 2-packs for cost-savings, but the 2-pack versions lack anti-vibration pads, so IMO it is worth it to get anti-vibration screws like https://www.amazon.com/Pieces-Rubber-Vibration-Flexible-Mount/dp/B00VRB3PJY/ or https://www.amazon.com/Noctua-NA-SAV2-Chromax-Anti-Vibration-Mount/dp/B018T3826S/ .

Y splitter cables if you don't have enough PWM headers on motherboard for all your case fans. https://www.amazon.com/Noctua-NA-SYC1-Accessory-4-pin-Y-Cables/dp/B00KG8K5CY/

If you decide to go Noctua, they are a bit more expensive than ML's, but come with anti-vibration parts. They also come in 3 pin and 4 pin versions, let me know if you need advice on which fans to get, and tell me where you would place them, i.e. case, heatsink/radiator. You can't go wrong with Noctua unless you hate their color scheme, really top notch quality with good accessories like anti-vibration screws and low noise resistor adapters.

If you want more affordable quiet fans, there are some options that are cheaper for similar or just slightly worse performance, but me personally, I recommend going for really good case fans, fluid dynamic bearing fans can last 10-20+ years of continuous use no problem and should follow you for many computer builds. I have tried a few other brands, and personally I am a big fan of Cougar Vortex fans that have built-in anti-vibration pads, $12 for 120mm, $18 for 140mm, and I think Fractal Venturi perform very similarly.

And remember to use motherboard to control your PWM fans, maybe set them to 1000 RPM and then raise them up or down as needed to make sure they aren't too loud themselves and to make sure there is enough airflow for GPU fans to not be loud.

The H500 is a low resistance case so you do not really need great performing fans. Just buy good looking and quiet ones and you are set to go. Extra high performing fans only makes a minor difference in the H500 cases. The Cooler Master RGB ones are great for this case no problem... They can be made quieter if you buy these silicone fan mounts that replaces the screws: https://www.amazon.com/Noctua-NA-SAV2-Chromax-Anti-Vibration-Mount/dp/B018T3826S/ref=sr_1_3_sspa