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@gbj_tester
It has 3 bolts because that's a way of getting the chain to clear the bolt heads on a 15T sprocket.
Worst case for a bolt on sprocket is likely to be a 2:1 drivetrain plus a heavy bloke on long cranks, applying 2000N at a radius of 180mm for 360Nm at the crank, reduced to 180Nm at the sprocket due to the gear ratio. Bad news on a 1.370"×24tpi thread, where the suggested tightening torque is about a quarter of that. The bolt circle radius is 22mm, so the shear load on all the bolts is ~16kN, and the material cross section is 12.5mm² per bolt. I think the suggested maximum shear load on grade 12.9 bolts is about 170N/mm² for cyclic loads, so 2100N per bolt, 6.3kN if all 3 share the load equally. This is ignoring any friction between the sprocket and mounting face, which is probably a reasonable assumption, and there are big safety factors in there to allow for a safe cycle time of 2 million cycles. So, a fat bloke doing a maximal standing start on a low gear won't snap the bolts immediately, and he can do 1 million revolutions at around 40% of starting torque before the bolts fail from fatigue. A million revs on a 52" gear at a nice low climbing cadence of 50rpm and 800Nm peak torque at the crank is 1900W peak power output, 8mph and 2600 miles travelled. We need somebody with a Watt bike to tell us the peak:mean torque ratio, but just looking at the polar graphs suggests to me that even absolute duffers manage about 4:1 and elites can get to 2:1, so average power output of 475W even for a clumsy fat mountain biker.