This impact grenade was an offensive grenade and functioned with a slightly improved "RG34" mechanism.
It was used throughout the cold-war period.
A fragmentation shell existed and would make it into a defensive grenade.

There appears to be two types of this grenade, an early manufactured type and a newer model.
There is no hole present in the top of the older type, also markings are different.
The old markings are in the same style as found on the older

Photos on the right and the four below © Cory.

old & new style compared:

Length :
Diameter :
Weight :
Filling :

Sectioned grenade and fragmentation-sleeve photos © Rob V.

RG4 with fragmentation cup :

Photos Jarda Mattás.

On my shelf, dated 1981 :

Shown on the right is the instructional version of the grenade.

Photo © Rob V.