Here's a trick so you don't have to buy a new pair every time one breaks
Step 1: Wrap a Wire..
Grab a thin wire that's about one and a half inches and wrap it once , tighten by squeezing it w/ pliers
Step 2: Put It In.. ;)
Step 3: Put the Stopper Back
Now with the stopper, if you lost yours you can use any sort of rubber or something just size it;
poke a hole in the middle and slide it down, then cut the excess but leave about 0.4 cm 'cus you're gonna want to bend that
Step 4: Bend It and You're Done!
Just use pliers to bend and it's finished!
This this fix is better than the old method of piercing the the strap or whatever it is with a nail because overtime it'll snap and it'll be unfixable