Violin 2 Prong String Adjuster Post-Type 4/4 Size

I don't know if I did something wrong but I purchased about 8 of these to install on two violins. I don't if I did it wrong because they cut through two of my new stings in the first month, maybe the strings had issues but I was a little worried so I removed them from my violin. I looked at them and tried to sand off any sharp edges. I have reinstalled them and they seem to be doing okay, for now, I wish I knew If I did something wrong or how to fix this problem for sure.

good