First Mention: LIAB Text 42
First Appearance: Hvs.tCF 2
Grenades are bomb magic items used by Charlescomm. Charlie kept them a secret until Charlescomm and Gobwin Knob entered open war. They work similarly to the Stupidworld equivalent. However, just like most magic items, they are resizable, and it would seem that their trigger condition is more sophisticated.
Ace Hardware made a magic item described with a very similar if not identical physical appearance when in the service of Jetstone. It's unknown why he didn't recognize it or find it familiar to the one he had previously made.
Real World References
See the grenade Wikipedia article.