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IS 3677:1998 is the Indian Standard (BIS) for fittings for copper and copper alloy tubes. IS 3677 covers fittings (elbows, tees, couplings) for copper tube systems. Capillary fittings are soldered/brazed; compression fittings use mechanical seal. Used in plumbing, HVAC, medical gas, and fire sprinkler systems.
Specification for capillary and compression fittings for copper tube systems in plumbing, HVAC, and gas installations.
Capillary: cheaper, neater, permanent, needs skilled installer. Compression: no heat, anyone can install, more expensive. Use capillary for concealed, compression for accessible.