Here's a pic of that lock I mentioned a while ago. Like I said I only recently discovered this hole and wasn't exactly sure it's purpose. I'm not so concerned about any theft issues but if this lock was designed as
an added safety bonus, in case the trailer decided to pop off, then I'll definitely get one. I was in the store today and saw their new couplers but the new couplers don't have these holes. These couplers are generic for larger utility trailers, horse and or construction trailers. This is not an RV store but a hardware/surplus store that sell RV type accessories. The store employee was swamped with other customers plus they were sold out of this lock.
At the bottom of my coupler, you'll see a quick pin inserted into a bolt (red arrow) I crafted, so to lock things. I doubt the bolt's tensile strength is very strong but I'm sure it would prevent the latch from moving. However if I am wrong, please free to correct my assumption.
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Jerry & Debbie
Ford Explorer 4.6 Triton V8, AWD, 4x4
1985 Sunline Saturn T-1350
Ham radio VE3JCJ, VHF, UHF and HF