I used 3/16" line for our jiffy-reefing lines. . .
Most modern yacht braids (not purchased at Canadian Tire) have a breaking strength similar to the same diameter in steel wire. A 3/16" reefing line is not likely to break. If you go any smaller, it may be hard to grip by hand. Smaller usually has 2 advantages:
- It's lighter (for the hardcore sailor/cruiser).
- It will be cheaper because you pay by the pound. A 3/16" line will be less expensive than the same braid in a 5/16" line.