Final answer:
Slack adjusters, part of heavy vehicle air-braked systems, should not exceed one inch of play for proper safety and braking functionality.
Step-by-step explanation:
The student is asking about the acceptable amount of play in slack adjusters, which are components of a braking system, specifically air-braked systems commonly found on heavy vehicles like trucks and buses. The standard amount of play in slack adjusters should not exceed one inch when pulled by hand at the point where the slack adjuster is attached to the pushrod. To maintain safety and proper braking functionality, it is crucial that the slack adjusters are properly maintained and adjusted according to the manufacturer's specifications.