Complex sentence: Torque wrenches do not give a direct measurement of the preload in the bolt, and indeed much of the torque applied is lost overcoming friction under the torqued bolt head or nut (50%) and in the threads (40%).
Split into simpler sentences: Torque wrenches do not give a direct measurement of the preload in the bolt. Much of the torque applied is lost overcoming friction under the torqued bolt head or nut (50%) and in the threads (40%).