Nut to secure fan blades on outdoor unit to Bosch Compress and Nordic Inverter PHR-N air to air heat pumps. nut is number 16 on image and fits following models:
Bosch Compress 5000 AA 5.0
Bosch Compress 5000 AA 6.0
Nordic Inverter 12 PHR-N S
Bosch Compress 7000 EHP 6.5 AA