We are sometimes asked "what is the strongest rosary?" This page attempts to address that and related questions.
There are three common materials used to construct a rosary:
Each has advantages and disadvantages. We tested each material using a hanging scale to see at what tension each would fail (break).
The cord we use (and tested) is dyed polyester. Polyester is not the strongest cord material, but it is good, has a nice feel, and holds color (and resists wear) better than most nylon. At about 1.5mm thick, it is too thick for use in most stone, glass and crystal beads. It is useful with wood, bone and plastic beads, and is among the faster materials for assembly. Of the materials we tested, the cord was the strongest, breaking at a square knot under 25 pounds of tension. I noticed some stretching before that, but it took real effort to break.
The strongest rosary we've seen (and make) is cord only, and is made from #36 twine or parachute cord. The paracord one is rated to break at 550 pounds stress. I have not been able to break it (without using a knife or other tool).
The majority of rosaries are made from wire, formed into links that hold together the various beads. The advantage to wire is that, when there is a break, it can be easily repaired. While a damaged cord rosary often requires rebuilding the entire rosary, a damaged wire rosary may require assistance at only a couple links. In our tests links began to deform at around 5 pounds of tension, and unsoldered chain links spread open. At that level, eyepins pull open and the rosary will literally fall apart.
Wrapping the eyepins and using soldered chain improved the situation. Deformation still began at 5 pounds, but the eyes elongated into ovals instead of popping open as they do with unwrapped eyepins. Above ten pounds wraps began to unwind, and soldered chain links cracked at their solder joints. This is much better than the common wire rosary, but considering the increased labor cost of a wrapped rosary, the increase in strength may not be proportional. "Bows" also begin to deform between 5 and 10 pounds, but last longer than end wrapped beads.
The material -- the metal -- used to construct the rosary doesn't make a whole lot of difference at these dimensions, but common sense prevails; for example, thick, half-hard sterling is going to hold up better than thin, dead-soft gold. Oh, and these so called "lock links" that people talk about adding to a rosary add no measurable strength.
Cable rosaries -- usually under trade names flexwire, accuflex and others -- approach the strength of cord rosaries. The cable is actually stronger, but breaks under a tension of roughly 20 pounds at the crimp points (similar to how a cord rosary breaks at its knots). The manufacturers advertise higher test strengths, and I don't doubt them, but the reality is that the crimping creates a weak point, cutting the actual strength down to about half of the test rating.
Cable rosaries cannot be coiled as tightly as wire or cord rosaries, or they will develop stress between the beads that will weaken and eventually break the crimps. Like cord rosaries, they also have the issue that, when they do break, they require complete reassembly. However, cable rosaries do work with a wide variety of beads, including stone, crystal and glass.
The cable has a nylon sheath that sometimes wears off with use, too. This doesn't really affect the strength of the rosary, but can be disconcerting.
The longevity of a rosary depends primarily upon how it is handled, the quality of assembly and materials, and the type of findings. A well-made rosary, made from quality components can last a lifetime, but will need maintenance. Eventually an eyepin is going to pull open, the cord will fray through or the cable will crack and break (probably at a crimp bead). But don't worry; all can be put back together again.
Having made easily over a thousand rosaries (as of this draft), we can only recall a couple that simply wore out with use; one was a "heavily-prayed" flexwire rosary that snapped at the crimp beads every few years, and the other was a large, heavy, hematite and wire rosary that was kept in a pocket during the day. Most that have needed repair did so as a consequence of obvious mishandling.