This Genuine Shimano replacement part may have multiple applications, but is primarily designed to be used in pairs to tighten the left crank of some Hollowtech crank arms to the driveside-integrated BB spindle. Shimano uses two opposing bolts for proper clamping force at 13-15Nm on most models.

When fastening the left crank arm, gradually tighten the bolts against each other, then set them to the proper torque specification. Do not tighten one all the way, then tighten the other and call it good. Always use a dab of grease on the threads when installing.