Thanks for the suggestion.
It is for a Baikal izh-94 Taiga so the number quoted for the rail is 12 mm, but this may be a European rounding thing.
Is the rail measured from top edge to edge?
Looking at Amazon, there is this adapter, that says it is for 11mm dovetail rails,
https://www.amazon.ca/daronde-tactiq...8Y3ZSXD32CWA98.