What safety device keeps a slotted nut from turning or coming off

Ir at sea level and 30°c and 50% relative humidity flows at a rate of 1 kg/s through a cooling coil that has an apparatus dewpoint of 10°c. the air leaves the coil at 15°c. determine the following: 3.1)- relative humidity of the air leaving the coil; 3.2)- moisture content of the air leaving the coil; 3.3)- sensible heat factor; 3.4)- total heat transfer rate; 3.5)- sensible heat transfer rate 3.6)- latent heat transfer rate