I probably shouldnt have, because now Im more confused than I was before. The issue. My 550XP came with a 16" bar. I wanted an 18. I ended up with a Tsumura .325 .050 bar, and a Stihl 23RS and an Oregon 20LPX chain. Both seem to work just fine for the last year or so. The thing is, its a short (height wise) bar. More @Wikipedia
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