Southco E3-7-1 triangle key, also called the "large triangle key" or the "8mm triangle key" by Southco. This is very commonly found on RVs, campers, boats, and other types of outdoor or weatherproof enclosures, for a type of lock called a push lock or compression lock. This key has a recessed / hollow triangle shape in the center of the cylinder that grabs onto the mechanism that opens and closes the latch.

This key is also used in many industrial applications, but we make no claim that this key is useful for any specific purpose besides opening an 8mm triangle compression latch. Please make sure that "E3-7-1" or "8mm triangle" is the same code as the key you need, as there is a very similar looking key called the "small triangle key" or "7mm triangle" that is not compatible with this type of key.