What damage can overtightening an MS flareless fitting cause?

• A. Overtightening drives the cutting edge of the sleeve deep into the tube and weakens it.
• B. Seals become brittle.
• C. Fastener threads strip.
• D. Tube expands and causes leakage.

Answer: (A)

Overtightening MS flareless fittings causes the sleeve’s cutting edge to bite too deeply into the tube. This weakens the tubing wall by thinning it, creating a point of reduced strength that can crack or leak under pressure. The seal in flareless fittings is metal-to-metal formed by the sleeve cutting into the tube, not a brittle elastomer or a separate gasket, so the risk isn’t seals becoming brittle. It’s also not about threads stripping or the tube simply expanding—the problem is the excessive bite into the tube wall. To avoid this, follow the manufacturer’s torque specs and inspect the tube for any scoring or thinning after assembly.