Cello cases are designed to allow you to carry your cello, keep you from bumping it into things, and protect it from mild weather. The cases are typically guaranteed against workmanship, but are not warranted to actually protect your cello from damage. Some of the worst damage that we have seen to cellos has been from them dropped due to failed strap hardware.
In the photos below, our customer shows us his recent failure.
"Hi Linda. Thank you for the safety cords you installed with my case! This just happened!”
We think that most of these strap hardware failures come from mishandling. When you throw your cello up onto your back in a twisting motion, this puts forces onto the strap's hardware that it was not designed to take.
In the first photo below, the green arrow indicates the typical failure spot. That metal is designed to hold something straight up and down. It is not designed to tolerate a twisting, or sideways motion.
In the third photo, you can see that there was metal fatigue failure. You can also see how the strap is twisted.
We highly recommend that you use the cables with your straps. If your cello case did not come with cables, we sell them on our website. When customers come to our store to purchase cellos/cases, we always install the security cables for them if they tell us they will be using the straps.
Your equipment should also be checked frequently. All hardware on a case is replaceable and will eventually fail; velcro, snaps, handles, clasps, D-rings, and especially your shoulder straps. When you install the security cables, use some LokTite on the threads to make sure they don't come unthreaded with use and vibration. And then check them weekly to make sure they are still threaded tightly. (a side note about velcro: "be a peeler, not a ripper!" if you RIP your velcro open every time, it will wear out much quicker. Gently peeling the 2 sections apart will give you many more years of service.)
Most case manufacturers are now supplying little threaded cables that are to be used as redundant security in the event of a failure of case hardware, or more frequently, strap hardware.
Musilia cases are the one exception; they do NOT use any metal for their strap system. They have a proprietary system using bars embedded in the case, and nylon webbing.
The green arrow indicates the typical failure point. We have actually seen some instances where the domed part has pulled out of the hole, but more typically, the metal breaks. The cable should be looped through your case D-ring along with the clasp.
You can see below that his strap hardware failed in exactly the place indicated in the first photo by the green arrow.