Only if the rotor head is designed for low clamp loads. Rotors typically require metal washers (NAS1149 or NAS412) due to extreme centrifugal forces. Check your rotor maintenance manual first.
Once you have obtained the official , you need to integrate it into your ISO 9001 or AS9100 QMS. nas523 pdf
If you need an insulating washer to prevent galvanic corrosion between a steel bolt and an aluminum airframe, you need NAS523 . If you need a load-spreading metallic washer, you need NAS412 or AN960 . Only if the rotor head is designed for low clamp loads