Why I’m asking? Never had an issue with the shaft coupling and never thought of it as a potential weak point. But a friend of mine lost one of his couplings (different and obviously poor design) this weekend while docking. Propeller shaft slipped backwards, prop damaged.
Fortunately no severe water leakage, stuffing box still working, and repair already underway. And fortunately it happened while the last docking of his vacation trip.
best regards / med venlig hilsen