This is the practice version of the RG4 impact grenade. It could be re-used after every excersise.
After resetting the impact mechanism the safetypin was sealed. A "VLOŽKA KOUŘOVÁ RG-CV 5" smoke charge was placed by the user.

Height: 85mm, unloaded weight: 350gram.
Diameters:
-cover : 57mm
-hole in cover : 15mm
-lower body : 53mm
-measured over mechanism : 65mm

Photos below thanks to Jarda Mattás.

Details below © Pascal :

All nine photos below © Milan.

It shows all grenade components including the cartridge that was to be replaced after every use.
The cartridge was inserted upside down so that the ignition was concentrated upwarts through the hole in the top cover.
White smoke was emitted for 8 seconds.

Data of the VLOŽKA KOUŘOVÁ RG-CV 5 smoke cartridge :

Body diameter : 15 mm
Body height : 25 mm
Rim diameter : 18 mm
Packing : 25pcs in a paper box