This is the splined adjusting lug for the inside of the rear 914 caliper. it is easily removed by cocking a long 4mm allen wrench in it. it is located under the inner adjuster cover which may have an allen socket or a 10mm bolt head to remove. extra long for an easy reach. adjusted through the swing arm, the pads need to have 8 thousands clearance between the pad and the rotor, and check the rotor for warpage.