Technically most Thread lockers depending on their viscosity can be used be used as thread sealants too because in effect both are based on same base chemical. However, viscosity and strength play a crucial role in the selection process and proper care must be taken. A low viscous thread locker may not be able to fill the thread gaps in pipe fittings and similarly some thread lockers (particularly high strength) can form permanent joint on fittings which may not be desired.