WHAT IS A GDM SWING LOCK ALSO CALLED ? BARREL, RATCHET OR VANDAL ? WE HAVE A TRUE COOLER MOD# GDM41SL
Not sure about "vandal" (a beefed up version of one of the other two?) but barrel and ratchet for any sliding door appliance, such as your True GDM-41, are just different types of locks (see pictures below, there are from True).
Barrel would have to be factory installed because it's cut into the door and its strike plate is in the body and seals and insulation are involved. A ratchet just mounts in-between the sliding panes to prevent them from sliding past one another. It's self-installed but it does affect the positive seal between the doors, so your refrigerated merchandiser may have to run a bit longer. It's pretty common though, so it does not seem to be that big of a problem for most people.
So, if you already have the cooler and it has no factory-installed lock, your only option seems to be what's called a "ratchet lock".
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