I have no idea other than one is .105" and the other is .095", but as you know, they are the same size side by side. Price is about the exact same for each. I was kinda wondering how the 223 would do since it didn't like the PST from a power need standpoint, but it runs it just like it runs Crossfire only the MST outlasts it by a mile and out cuts it too. MST is the single fastest cutting line I have ever used. I rarely have to bump the head now doing all the chain link like I have had to do with Crossfire and most other lines.