This grenade is an exact copy of the French OF.
The diameter of the threads (15mm) accept the French or Russian fuzes.
It is not the same grenade as the "Ofensiva Polaca" which has larger "polish" threads.
Photo shows grenade with a Koveshnikov fuze.

Length body : 100 mm
Diameter : 61 mm
Weight : 150 gr.
Filling : nitrate mixture

Photo © Francesco.