The number of "teeth" on the drive sprocket/drive rim. More "teeth" translates to higher chain speed, at the expense of torque. 7 pin/teeth is what the factory puts on them. You can replace the rim with an 8 or maybe even a 9 depending on what bar length you're running. My 394 pulled a buried 32" through hackberry today. 7 pin rim. I don't know that it would have been happy with an 8 pin on it at that length, someday I'll have to swap it out and see.
My wife's uncle was supposed to cut this up, the existing cut you see in the round that the saw is setting on is from his MS290. I guess he decided he really didn't have enough saw.
The tree was cut down by someone else. I helped them split a couple 16' trailer loads of it.
I cut a couple of slabs off so I could set the 1/4's on them and keep my chain out of the dirt. I don't know how many cutters are on 105DL of chain, but it's more than I want to file. I put the 24" back on after I was done so I could fit it in the jeep.