These grenades were used by the republican army before 1945.
Early grenades were fitted with the Spanish Billant, later types carried the B-3 fuze
The Billant-version had larger threads than the French, and a straight lever.
It could be launched by hand or rifle but also (by means of a connecting tube), like a mortar.
To ensure that the gases of the shot were propel the grenade, it has the lower body part in the shape of a disc.
Grenades fitted with the B3 fuze were hand-thown only.
Photos below and info © Dani.