The Mk2 (MkII) fragmentation grenade, US production. Weight: 1 lb 5 oz (0.6 kg)
Used by the US armed forces during World War II and in later conflicts including the Vietnam War. It was phased out gradually, the US Navy being the last users. It was generally replaced by the M67 and M61 grenades.
The Mk 2 was commonly known as a "pineapple" grenade, because of its distinctive shape. Grooves were cut into the cast iron shell to aid in gripping the grenade - this provision gave it the appearance of a pineapple fruit. A common misconception is that the grooves aided fragmentation of the grenade, which they do not. Although TNT was used as a filling, EC blank fire (smokeless firearm) powder was also used instead in some models due to the tendency of TNT filling to over fragment the cast iron body. EC powder produced an adequate amount of fragments and did away with the need of a detonator. The detonator was initially replaced by a small length of safety fuze terminated with a black powder igniter charge. Production grenades with the EC powder filler used the M10 series of igniting fuze.
Reference from Wikipedia.
Normally a yellow band will be at the top of grenade body indicating high explosive filler. Fuse is M228, late production type.