I bought a bundle of coins which included a coin that at first glance looked like Egypt > 10 Qirsh > 1966.
But it felt very smooth, warm, and low weight. I checked: 24mm diameter, 1.7gms. Very under-sized. I suspected a counterfeit coin - not surprising since these are silver coins. Call that thesis A.
However, it also has mint markings on the rim which are unknown to me. I wondered if counterfeiters would bother to mark a fake to distinguish it from a real coin. Secondly, I noticed that the coin copies the real item except it has no 'مصر' (Egypt) above the amount. Again, would criminals be so scrupulous? This made me think the coin was an official issue. I thought it might be an essai but the date is the end of the official issue not the beginning - unless this was an early model of the 1967 coin discarded in favour of the design they actually used? That 'official' look suggested it might be a tourist token not currency - perhaps for mint visitors to buy as a souvenir? Did they do that in the 1960s? Call that thesis B.
Is there a thesis C? I invite you to offer your own opinions.
Here are the best photographs I could manage - the surface is very smooth, hard to capture details.
Thank you for your interest :-)
Sorry, I identified this as a standard 10 Qirsh from 1967. Not 1966. My mistake - mixed up the translation from Hijra to Western calendars. Oups!