The easiest thing to do is to pinch the nut lock washer with the nuts on the shaft part of the stud bolt and tighten with the fingers.
You can feel that there is no looseness unless you apply torque several times the fastening torque.
Change from original brake caliper to 4 pot caliper, and dedicated bracket one off. I got the tip of another company's genuine caliper fixing bolt to be cut off, but when tightening with specified torque ... a slight tip protruding ... Although normal washers will suffice, they are also important security points so purchase here. It is satisfactory because the jumping out is eliminated and it will also prevent looseness.