The flexinut fixes into an 8 mm diameter hole and is tightened with a single screw. No plain washers, lock washers or nuts. Cannot vibrate loose. An internal fan can actually be fitted from outside the case.
Unit comprises a rubber flexinut and screw. M4 x 20 mm
Note. Only suitable for 80, 92 and 120mm fans due to the requirement for drilling 8mm mounting holes.
Sold in a pack of four.