The description for this coin was: ar-Râdî billâh, 322-329 H./934-940 AD.. Donative dirham no date and mint, struck as a centre impression of dies for double dirhams 325 H. Is it a correct information? Because I can't find any Abbasids coin with such centre. Does anybody know where to find a photo of ar-Radi's dirhams?
The following page has a number of dirhams from Ahmad ar-Radi, but none are donative and do not show the style of script on your piece: http://www.zeno.ru/showgallery.php?cat=3049 The only donative dirham picture I could find is from al-Muqtadir (AH 295-320), the obverse of which is very similar to yours in style and layout (ignoring the outer inscription), but with Muqtadir's name on the second line instead of Radi.
The writing has no diacritical marks, but I'm guessing the following: OBV: lillah (for Allah) ar-Radi (ar-Radi) billah (in the name of Allah) REV: amir al-mu/ minin all three reverse lines would translate as: commander of the faithful
