This Czech grenade should actually be called "The mother of all impact types".
It's great design was copied and altered throughout Europe and appeared to be very succesful.

The original Czech name for the grenade is OUG vz34.
It had an "always"-fuze which would detonate the grenade without delay.
When thrown, the safetyband would unwind, freeing the striker.
On impact, the striker would penetrate the primer no matter what side it fell on.

Photo © Jarda Mattás.

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Shown below is the throwing dummy which was used for training.
This training grenade was called SUG vz34.
The body was much thicker steel but almost identical in weight.
It was painted red for identification and it could be used many times.