The head of Meterguard's barrel lock is short enough to lie completely within a shallow recess such as this. The tapered head cannot be gripped with pliers, and it will not break off.
Meterguard's barrel lock is water tight; is made of through hardened stainless steel and is guaranteed not to rust.

In this particular application, a standard length Meterguard barrel lock does not pull itself tightly against the housing and is therefore free to rotate within the recess.

For more information and photos on how well the "O" rings and stainless steel perform in the "real world", click on Environmental Test.