Having finally available the first porcelain piece to try with the interlocking I had the pleasant news that the designed interlocking worked perfectly. Despite this there were some changes to be made in order to make the lamp stay in the right way and, the two fins for the interlocking, were slightly too long and therefore had to be shortened.
So I printed the first model with the bronze filament and the interlocking both in front and behind making some small changes compared to the tests made in Italy.
The new model fits perfectly the lampholder and makes the thread enter the box that closes well but that, in the lower part, still leaves a small lateral movement.
Unexpectedly, one of the tongues has broken because in the porcelain opener there is an internal part where the thickness increases slightly and then it has to be raised further by 1 mm.