This grenade was produced as a part of it's chemical weapon arsenal.
Just like the other ex-yugoslavian chemical hand and rifle grenades, this grenade is also marked as SCHOOL, with yellow band glued on the middle of its body.
It is filled with live chemical agent 2-chlorobenzalmalononitrile also known as CS-1.
The grenade was produced in the factory TRAJAL in the city of Kruševac from 1979.
The body consists of two equal rubber parts glued together. On the upper part of grenade body there is neck with thread for its fuze.
Below the thread, a rubber shell is glued for the explosive filling (5 grams of Pentolite).

Information and photos below © Goran.

The fuze is the same as on M75 grenade, only the lever has different shape to fit on BRS M79 AF-1 body.
On the bottom part of the body there is a hole through which chemical agent was filled in the factory. That hole is shut with small rubber cap.
The body is made of black rubber, painted in standard Yugoslavian people's army olive grey colour.
On the middle of the body,over the seam of upper and bottom part of grenade body yellow band is glued which symbolises that it's a school grenade, but of course it is not, it is live filled with live chemical agent.

Each grenade is packed in nylon bag to prevent leaking CS-1 gas and then in plastic transport can which also has a yellow band glued on its upper part.
After activation, fuze and detonator activate the explosive filling which splits the grenadebody and spreads CS-1 chemical agent in the form of aerosol.

Total length : 108mm
Diameter : 75mm
Weight : 236gram
Filling : 112gram CS + 4gram Pentolite.
Fuze delay : 3 - 4 seconds