About the Raffaello Slug 20 rail mount bolts

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Does anyone know the specifications of the rail mount screws for the Raffaello Slug 20?

Benelli factory rail kit comes with screws, but these are short ones to secure it to the upper receiver.
The Raffaello Slug 20 can be secured to the barrel across the receiver, but I could not install it because I do not know the specifications of the screws.

If you know the length, thickness and pitch, could you please let me know?

Thanks.