This a practice version of the Soviet RG-42 offensive blast grenade made by the Polish.
The casing is made of heavy steel sheet metal with gas escape holes and a base that unscrews with provisions for attaching a simulation charge. It is reloadable and apparently has a rust resistant paint applied to the inside.
The RG-42 hand grenade appeared early during WWII as primarily an offensive munition.
It's body is also made of sheet steel, but with an internal multilayer fragmentation liner.
The UZRG fuze (3.2-4.2 sec) was standard.
With 118g of TNT, it produced a 20 meter effective casualty radius.
It continued to be made after WWII by numerous Warsaw Pact and other communist countries.
At left is a WWII RG-42 with its transport plug. The fuze was not inserted until just before use. Color is olive-green with black makings.
(Grenades painted black with a white band have been observed. Probably Soviet made training grenades?)
To the right is a modern (1970 dated) RG-42 made in Bulgaria.
Seems there is a slight difference in the fuze bushing, compared to the WWII version.