3 or 4 Pin Fan Headers [for PC fans]

thingiverse

Simple semi-working 3-4 pin fans are available. They feature a built-in collar or raft, which is often necessary when printing small parts that may not stick to rafts on their own. Avoid printing these fans with supports altogether - instead, make sure the collar part rests directly against the build plate. It's also worth noting that it's possible to insert the plug in reverse order. A notch is present on one end of the plug to help indicate its proper orientation.