On January 24th, it was reported that after multiple airlines reported finding loose components during inspections of grounded 737 MAX 9, Boeing issued a notice to its suppliers last week outlining the practice of ensuring proper tightening of bolts.
This memo dated January 17th shows that Boeing requires suppliers to "must" meet quality requirements, stating that "ensure that work instructions are error proof and continuously monitor quality, especially torque requirements.". Boeing has requested suppliers to record torque requirements in their work instructions and mechanics to record the torque applied when tightening components, and to ensure that tools are properly calibrated to ensure that bolts are properly tightened. (Reuters)