This is the American M26, a High-Explosive-Fragmentation (HE-Frag), Anti-Personnel (AP), delay (DLY) detonating, hand-grenade which has a notched fragmentation coil liner including the M26A1, A2 and A3 and is manufactured in various countries.
Its distinct lemon shape led to it being nicknamed the lemon grenade. The M26 hand-grenade is externally identical to the M26A1 which uses the M204A1 fuze. The M30 is the practice version of the M26 and M26A1 hand-grenades. The M61 is the M26A1 with an extra safety-clip, called the jungle clip which was attached to the safety lever to prevent the safety-lever from flying off unintentionally. he safety-pin is removed freeing the safety-lever, which is held in place manually.
When the hand-grenade is thrown, the safety-lever is released and forced away from the hand-grenade body by the spring-loaded striker. The striker Impacts (IMP) the primer, which ignites the 4 to 5 sec DLY, initiating the explosive-train.