When a metal fitting has a hole drilled through it the hole is filled with?

When a metal fitting has a hole drilled through it, the hole is typically filled with a material such as a plug, sealant, or a threaded insert, depending on the application. If the purpose is to create a seal, a sealant may be used to prevent leakage. For structural reinforcement, a threaded insert can be used to accommodate a bolt or screw. In some cases, the hole may simply be left open or capped, depending on the design requirements.