Solo 96 Narrow-Wide Chainring

It is Shimano's four-bolt pattern where the bolts are not spaced evenly around the circle — that uneven spacing is what "asymmetric" means, and it is why a 104 BCD ring will not go on. Look at the ring currently on your crank: four bolts spaced evenly means you want the Solo, visibly uneven spacing means this one. If you are unsure, measure the bolt circle rather than go by the crank's model name — naming across Shimano generations is not a reliable guide.

30T, 32T and 34T, at 40g, 48g and 55g respectively. The choice is gearing rather than fit — all three bolt to the same crank, so nothing about the installation changes. 32T suits most trail riding on a wide-range cassette, 30T is the one for steep ground, and 34T is worth taking if you spend time on flatter trails or ride at an XC pace.

Only the bolt pattern. Both are 7075 narrow-wide rings with stepped bolt holes and the same 9 to 12 speed compatibility; the Solo fits evenly spaced 104 BCD cranks, this one fits Shimano's asymmetric 96mm pattern. Neither will go on the other's crank, so this is the one specification you have to get right before ordering — everything else about the two rings is the same.

Usually not. The alternating narrow and wide teeth fill the chain's inner and outer links so it grips the ring rather than bouncing off it, and with a clutch derailleur most trail riders never drop a chain. A guide is still worth fitting for downhill, bike park and racing, where a single dropped chain is expensive — the Zippa Lite ISCG05 adds that for 30g if your frame has the tabs for it.

9 to 12 speed. The tooth profile is cut for that whole span, so the ring does not need to match your drivetrain's speed count — it is the same ring whether you run 11-speed or 12-speed. Make sure instead that the bolt pattern matches your crank, because that is the part that actually decides whether it fits.