Take your radiator into your local hardware store...bring a fan as well so you know what length and what screw diameter/threading to get. There's also a screw threading guide in the sticky that illustrates the appropriate screw threads to use with many common radiator brands.
I've hauled all sorts of radiators, pumps, reservoirs, etc to the hardware store to find the exact matches I'm looking for. This is a lot simpler than trying to measure, write it down then drive home only to find out you got something a bit wrong.
i just got my radiator with 8 screws, 4 screws are 1/4inch long, and the others are 1 1/4 inches, are the short screws to hold my radiator to the case and the long ones to install my fan?
it a single xspc 120mm radiator i will install to the inside back of the computer
Doing it that way, you would use the short screws form outside the case, through the panel and into the rad, and the long screws on the other side through the fan and into the rad,
there are many ways to mount rads and fans, sometimes you just need to be a little creative
Just make sure you don't buy screws that are too long or tread them into the radiator tubes behind the screw eyelets. Some rad designs are offset to avoid this, some are not, so make 100% sure you take the safe road here. If a screw is too long, you can always cut it- there are a couple ways to do this, but this is how I do it:
-Mark your screw/bolt with a sharpie marker where you need to cut.
-Thread 2 nuts onto the screw/bolt higher than the cut toward the head of the screw/bolt
-Make your cut with bolt cutters or cutoff wheel.
-Un-thread each nut one at a time to clean and cut the end threads and check by threading the nuts back on.