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

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.

Rega does sell a torque wrench. It's $275 USD. It's included with their Aphelion 2 cartridge but available separately on Music Direct and other audio websites. I don't see it listed on the Rega website however.