Typically on Hollowtech II systems.
Pre load crank arm bolt cap M20 Shimano Hollowtech 2 Crank M20
CRANK ARM INSTALL REMOVAL TOOL PRELOAD TENSION SHIMANO HOLLOWTECH 2 II TL-FC16
CRANK ARM TOOL PRELOAD TENSION INSTALL REMOVAL SHIMANO HOLLOWTECH 2 II TL-FC16
Crank Arm Cap Preload Removal Tension Install Tool Shimano Hollowtech 2 II BLACK