The grenade was an inner can of explosive with an outer can of metal fragments or ball bearings. The heavy pattern No 9 grenade contained more HE and more shrapnel.
The fuse was ignited by a friction device or a cigarette.
Initially when demand for grenades was at its greatest, engineers were encouraged to improvise their own grenades from the tins containing the soldier's ration of jam, hence the name. Incidents with the improvised form and the supply of superior grenades led to official withdrawal of the design.