We've tested this MasterLock coupler lock to see if it is truly universal for vintage trailers. We have found that it is close to being universal, but not quite. The only coupler it doesn't fit that we've found is the type with the dramatically rolled front lip used on 50s and early 60s Airstreams. If your coupler says Marvel on it, this is a great fit.
The ball part of the lock slides in and out to create a snug fit. The inside portion of the lock is designed with ridges that contour many styles of coupler.
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