Hand Grenade Cutaway Drawing, 1951
It’s a fairly simple killing device: a metal container that contains “filler” (as the cutaway says) segmented so that it will split open in predictable chucks.
Here is what a generic 1950s hand grenade looks like, cut in half. The only difference between the two versions of the hand grenade is that the second one shows the safety pin ring removed and the safety lever raised. Thus, the striker (circled) is allowed to rotate and light the timed fuse.
Source: Popular Science November 1951