The central shaft is M10x1 metric fine thread. This nut is not really needed, and if present should be torqued only lightly, as too much torque can drive the prop drive up the taper on the crankshaft and destroy the design axial play and/or break the M8 thread at the end.
The prop holding bolts are 6x  M4. A 3Nm torque is more than enough for any prop.