Russ,
If you don't want to put too many keys on it, I use a Ti and Brass screw link from CountyComm
http://www.countycomm.com/tiscrewlink.html I have several and all but one lock very securly. They are much smaller than what you have discussed ....
i actually looked at my key ring and that is what i have been using for years. never accidentally screws apart - the knurled locking cylinder is not much larger than the biner itself.
two thumbs up!
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“Everyone should have a horse. It is a great way to store meat without refrigeration. Just don’t ever get on one.”
- ponder's dad