A mechanical engineer has told a trial that components linking a truck and trailer - which failed and led to three deaths - had worn over time.
William Kennedy gave evidence on Friday in the trial of Heavy Mechanics in the Wodonga County Court.
The Wodonga business serviced a BP tanker trailer and truck before the crash at Staghorn Flat on August 7, 2014.
The coupling failed and the tanker hit two cars, killing the occupants.
The business has pleaded not guilty to one charge of failing to ensure people were not exposed to risks to their health and safety.
Mr Kennedy held the trailer components in court and pointed out wear to jurors.
He pointed out "prolonged wear" which he said showed parts were "moving for a period of time".
IN OTHER NEWS:
Mr Kennedy said a nut, which the prosecution had said was central to the case, had a distorted thread.
He pointed out damage to an item known as a "boss", which is attached to a section of the tanker trailer, and housed the coupling.
"You can see the wear factor present," he said.
"This has been happening for a period of time to cause this wear."
The wear was a result of the nut being insecure, he told the court.
The tow eye would have moved up and down, sideways, longitudinally and rotated, he said.
Prosecutor Andrew Palmer, QC, had earlier told jurors it was vital there be no movement.
Director Keith Haire previously told the court he would perform tug tests to ensure there was no movement.
Mr Kennedy said that was "absolutely not" a way to assess wear to a tow eye coupling, which he said was a "critical part".
"It's not a reliable method."
David Padfield conducted tests on the components after the crash.
He repeatedly said wear on the components had likely occurred over time, due to there not being enough clamping pressure.
He put two components together but said they weren't a snug fit, which he said would lead to movement and eventual failure.
Former Heavy Mechanics employee Richard Trethowan told the court the business was "highly regarded".
"Everyone knows that we do a good job, I guess," he said.
He agreed the company was competent, safety conscious and professional in the four or five years he worked there.