Shimano FC-M521 middle chainring replacement What exact torque should be applied to secure the double gear fixing bolt (Y-1FM98020) ? !Double gear fixing bolt And what tool is usually used to fix the nut without damaging it while tightening the bolt? !Double gear fixing nut

According to the Big Blue Book of Bicycle Repair, Shimano steel chainring bolts 70-95 inlbs. Aluminum 44-88 inlbs. A Park Tool CNW-2 chainring tool or similar is used to hold the slotted nut and an allen wrench turns the bolt. Depending on the size of the chainrings you may be able to use a slotted screwdriver to hold the nuts.

!Park CNW-2