Here is a pic of how the piston stop must be placed to work properly:
It must be pinched in the squish band where the edge of the piston is strongest.
If it gets broken most likely you stuck it through the open exhaust port and now the edge of the piston cuts it off, and it may damage the piston by bending down the ring land in the process.
I got a saw today where the guy used a threaded in piston stop and he punched a hole in the top of the piston. It is not very thick there on the newer design engines.
The reason the MS 192 T and MS 200 T has a piston stop included by STIHL, and intended to be given to the end user, is because these saws have an outboard clutch, where most other STIHL saws have an inboard clutch, so all you need to get to the sprocket is the little orange screwdriver that comes with the saw. The instruction book does walk you through how to use the piton stop to remove a clutch for changing the sprocket on outboard models.
STIHL makes three piston stops, the angled one that comes with a 200 and 192, in black and white, and one that is set at a ninety degree angle for engines that have the plug straight up out of the top of the cylinder, like on some trimmers. The third one is plastic with a aluminum end and is for the newer engines that use a 10mm spark plug.
For all you 192 users, get in the habit of checking the muffler bolts often.
This saw is not a true "pro" saw, in my opinion, which is of course why it costs less, and the muffler is held on with self threading screws, not machine screws. The first time the muffler is installed a lip of metal on the muffler gets crushed down to form a gasket seal, and the muffler should rest on two little cast protrusions on the end of the cylinder to support it. If the screws work loose, then the muffler starts rattling around, wearing off the two supports, and the flat surface of the cylinder where the muffler seals. I have seen enough material get worn away in this area that when the screw finally does get tightened back up, it pushes through the cylinder wall into the piston.
I have a 192 T and rear handle and I agree that they both are great little saws. Any more with my torn shoulder, arthritis, and other getting old ailments, I usually end up grabbing one of them for the little odd cutting job around the house. For pro use just do your maintenance regularly and check all the fasteners.
I don't want to get in an argument with anyone here, but if you use an air impact on the clutch on a 192 it is very likely the flywheel key will get sheared on the other side of the crank. Also remember that modern saws have 2 or 3 piece cranks and an impact gun can loosen the press fit of the crank parts. I used to use an impact on the older saws but since I have personally messed up a couple of the newer models I now use the piston stop, a breakover, and steady downward pressure to remove a clutch or flywheel nut so I do not have to worry about any other damage.
Eddie