The sunvisors are, under the leather and padding, two sheets of aluminium that are rolled at one edge to form an internal diameter of 6mm. Four stainless rods (two for each visor) of about 10cm length and 6 mm diameter are flattened at one end, shaped, drilled and countersunk to accept the screws.
These rods are a tight fit in the rolled edge but can be rotated or moved in and out of the sunvisors to match any possible manufacturing variation in the screen frame. Note that there are four additional 10mm spacers to distance the visors from the screen frame. If the visor has a tendancy to fall down the rolled aluminium must be tightened on the rods. I have managed to do this with a bit of scrap leather as padding and a wooden drift hit with a hammer.
I strongly recommend that that the visors be suitably upholstered to avoid accidental scalping in the case of an accident