Rega Apheta 3 on Rega Planar 8:  Any idea on screws torque values ?

Per Rega the Aphelion 2 torque is (0.4 Nm)

You might want to ask the distributor in your country (or closest country) for info on the Apheta 3. 

Here is a list of global Rega distributors: Rega Dist

depends on the cartridge body undergoing deformation under load . Common sense is a good guide..

I remember that Rega used to sell a torque wrench set for their cartridges.

II asked my distributer to check with Rega.

In the meantime, as advised above, I will close it very gently just so it does not move.