The value given by 3W of 40 inch/pounds is based on the ISO standard for the M5X.8 bolt and has nothing to do with the compressable material behind it. You can do a search on the net for a torque value chart which gives standard torque values for each size bolt. If you can't find a metric chart just look up a 10-32. Props made of European Beech Wood have the following properties. Note the low density and great difference in Compressive Yield Strength based on the attitude of the grain to the load. That's what causes the problem.

Physical Properties Metric English Comments
Density 0.660 - 0.780 g/cc 0.0238 - 0.0282 lb/in³
Cell Length 1.10 mm 0.0433 in Mature Wood

Mechanical Properties Metric English Comments
Hardness, Wood Indentation 4800 N 1080 lb (f) Side
Tensile Strength, Ultimate 3.50 MPa 508 psi Perpendicular to Grain
130 MPa 18900 psi Axial
Modulus of Rupture 0.104 GPa 15.1 ksi Static Bending
Flexural Modulus 13.13 GPa 1904 ksi Static Bending
Compressive Yield Strength 7.90 MPa 1150 psi Perpendicular to Grain
46.0 MPa 6670 psi Parallel to Grain
Machinability 100 % 100 % Good Relative to Other Wood
Shear Strength 12.3 MPa 1780 psi Orientation Unknown
Toughness 31.2 J 23.0 ft-lb 2 cm x 2 cm sample
Cleavage 9.10 kN/m 51.9 lb/in

Thermal Properties Metric English Comments
Shrinkage 0.100 - 1.10 % 0.100 - 1.10 % Axial; Green to Zero Moisture
8.60 - 18.2 % 8.60 - 18.2 % Tangential; Green to Zero Moisture
12.3 - 21.8 % 12.3 - 21.8 % Volumetric; Green to Zero Moisture
5.80 % 5.80 % Radial; Green to Zero Moisture

Descriptive Properties
Color Whitish to pale brown Usual for heartwood
Pinkish-red Steamed; Usual for heartwood

Now can we get back to the DL-50???