When you say "Baseball Grenade," you are most likely referring to the M67 Fragmentation Grenade, the standard-issue anti-personnel grenade for the U.S. military since the Vietnam era. It earned its nickname due to its spherical shape and size—roughly 2.5 inches in diameter—which was specifically designed to be easily gripped and thrown by soldiers who grew up playing baseball.
The Shape: The spherical design is not just for ergonomics; it allows for a more uniform distribution of fragments upon detonation compared to the older "pineapple" (Mk 2) or "lemon" (M26) designs.
Internal Composition: The M67 consists of a 2.5-inch steel body packed with 6.5 ounces of Composition B (an explosive blend of RDX and TNT).
Fragmentation: The steel body is designed to shatter into numerous high-velocity shards. It does not use a pre-segmented sleeve; the casing itself becomes the shrapnel.
While the M67 is the famous one, the T13 Beano was an experimental grenade developed by the OSS during WWII with help from Eastman Kodak.
The Concept: It was weighted and shaped exactly like a baseball so that an American soldier could throw it with maximum accuracy.
The Trigger: Unlike the M67's timed fuse, the Beano used a pressure-sensitive impact fuse.
The Failure: It was pulled from service because the impact fuse was notoriously unreliable—often detonating if the soldier accidentally dropped it or hitting a soft surface and failing to explode, only to detonate later when handled.
Modern baseball grenades like the M67 utilize two safety measures:
The Safety Pin: Pulling this allows the lever (the "spoon") to be released.
The Safety Clip (The "Jungle Clip"): A wire clip that wraps around the lever as a secondary backup. This was added to prevent the pin from being snagged by brush or equipment in the field.
Correction/Safety Note: Contrary to Hollywood portrayals, "cooking off" a grenade (holding it after releasing the spoon) is extremely dangerous and strictly prohibited in military doctrine due to the inherent variability in pyrotechnic delay fuses.
The M67 replaced the M26 "Lemon" grenade because the M67 was easier to throw in a "fastball" style, allowing for greater distance and better accuracy when clearing rooms or trenches.