Use 16 mm long 3M stainless steel bolts, stainless steel washers and nylon washers. Re-use the springs from the plastic stays. The items will be assembled in the order shown from top to bottom:

(1) bolt; (2) metal washer; (3) spring; (4) heatsink; (5) PCB; (6) nylon washer; (7) metal washer; (8) nut.

If for some reason the springs have been lost, you can use a spring from a ball point pen. Cut out a section about 1.5 cm long.