The M61 is the M26A1 with an extra safety (called the "jungle clip") attached to the safety lever.
This is to prevent the safety lever from flying off and allowing the striker to function if the safety pin gets accidentally pulled out by snagging it on jungle vegetation.

The most common method of carrying grenades was by straps on the ammo pouches.
Soldiers, inspired by characters in movies and TV shows, also commonly hung grenades on their persons using the safety levers, although it is said that "official policy forbade the practice as unsafe."
The M61 is the M26A1 with an extra safety (called the "jungle clip") attached to the safety lever. This is to prevent the safety lever from flying off and allowing the striker to function if the safety pin gets accidentally pulled out by snagging it on jungle vegetation.
The most common method of carrying grenades was by straps on the ammo pouches. Soldiers, inspired by characters in movies and TV shows, also commonly hung grenades on their persons using the safety levers, although it is said that "official policy forbade the practice as unsafe."
M26 grenade