You can still use them, just connect to the first 3 pins and leave the fourth unconnected.
Three pin fans have Pin1: GND, Pin2: 12V, Pin3:Sense (speed feedback)
Four pin fans have Pin1: GND, Pin2: 12V, Pin3: Sense, Pin4: Control Signal.
The Locking clip on the 4way sockets should still be the correct size for a 3way plug and will be offset towards pin 1. If they have no clip, then pin 1 will be marked on the PCB, usually with a little white arrow.
Bryce.
Three pin fans have Pin1: GND, Pin2: 12V, Pin3:Sense (speed feedback)
Four pin fans have Pin1: GND, Pin2: 12V, Pin3: Sense, Pin4: Control Signal.
The Locking clip on the 4way sockets should still be the correct size for a 3way plug and will be offset towards pin 1. If they have no clip, then pin 1 will be marked on the PCB, usually with a little white arrow.
Bryce.