Here is some information in English if that helps.
Rucni Granaty vz 21
The vz21 was in Czech service from about 1921 until adoption of the OUG vz 34 although manufacture ended in 1926. It was a dual-purpose grenade that could be used by hand or fired from a vz23 discharger cup as a rifle grenade.
The body is made of thin sheet steel in an elongated egg shape. The body is formed so that there is a central well running the length of the grenade from the top. The space between the outer walls of the body and the central well are filled with the main explosive filling. A detonator assembly consisting of a detonator and booster are fixed in position at the bottom of the central well. A primer assembly is located directly above the detonator assembly. The primer is fixed in the assembly in the centre. A weight with the striker mounted is located at the top of the well. A distance pin located in a small hole on top of the primer assembly prevents the weighted striker from coming into contact with the primer. A partially compressed spring presses down on the weight keeping the distance pin in position. A key fits in through the top of the grenade locking the pieces in position to ensure safety. The key has a small projection on one side that contacts notches in the top of the grenade ensuring that the key does turn accidentally. The key requires a turn of 360 degrees to remove.
There is a small lug formed near the bottom of the grenade, this is an indexing pin for use with the vz23 discharger cup. This ensures the grenade will rotate end over end after launching.
There are stamped markings on the top of the grenade giving the lot number, year of manufacture and a manufacturers mark.
When the key is removed, the parts are free to move, but are held in position by the partially compressed spring. Once removed, if necessary the key can be replaced to make the grenade safe. The grenade must be thrown so that it rotates end over end. When the grenade is thrown centrifugal forces cause the weight to move outwards further compressing the spring. When the weight moves out, the distance pin is free to fall out of position in effect arming the grenade. When the grenade impacts, the centrifugal forces stop allowing the spring to reassert itself and push the weight and striker toward the primer. The striker impacts the primer causing it to fire. The primer flashes into the detonator which explodes causing the booster to fire which in turn causes the main explosive filling to detonate.
If the grenade was not thrown with enough force, the spring would not compress enough to allow the distance pin to fall out.
TYPE- Offensive
WEIGHT- 450 gm
DIAMETER- 50 mm
LENGTH- 110 mm
FILLING- 125 gm
IGNITER- Impact
