A gas turbine engine blade root shim for use between a composite blade root and a wall of a slot in a rotor includes a longitudinally extending base having distal first and second transversely spaced apart ends, first and second longitudinally extending legs acutely angled inwardly towards the base from the first and second ends, and one or more apertures disposed through each of the longitudinally extending first and second legs. Apertures may include rectangular slots having rounded edges along the first and second outwardly facing surfaces of the first and second legs respectively and/or rounded corners between the first and second outwardly facing surfaces and the first and second inwardly facing surfaces of the first and second legs. Low coefficient of friction coatings may be disposed on outwardly facing surfaces, of the legs. Coatings may include polytetrafluoroethylene powder dispersed in a resin binder and other coatings having polytetrafluoroethylene.