What should be applied to male threads when sealing joints?

Male threads should be sealed with joint compound or tape to ensure a tight, leak-free connection. Joint compounds and tapes are specifically designed for pipe threads and help fill any gaps between the threads, creating a secure seal that prevents leakage of water or other fluids.

Using joint compound or tape also makes it easier to disassemble the joints in the future if maintenance is necessary, without damaging the threads. These materials are effective in accommodating the slight imperfections or variations in thread pitch and surface, which is crucial for the integrity of the seal.

The other options, while they may provide some level of sealing or lubrication, are not suitable for sealing threaded joints in plumbing applications. Welding material, for instance, is inappropriate for threaded connections that need disassembly. Grease may provide some temporary lubrication but is not effective in preventing leaks. Plumbing sealant is typically used for smooth surfaces rather than threaded connections, making joint compound or tape the most effective choice for male thread sealing.