LENS manufacturer Essilor celebrated 40 years of production in Thornbury with its staff, former employees and customers.
The company even stopped work for one day so the anniversary could be marked throughout the factory.
Essilor employs some 330 staff at its Cooper Road site, many of them local and a number who have given more than 20 years of service.
For the special event, their former colleagues and company pensioners were invited back to see how the factory had changed and to share memories of their time with the firm.
Thornbury is the headquarters of the company's UK operation and makes thousands of ophthalmic lenses every day, mainly for the independent market.
Managers also wanted to recognise their customers' contribution so organised an open day to give them the chance to see how the lenses were made.
During the celebrations, Thornbury mayor, Guy Rawlinson, unveiled a plaque to mark the anniversary of what is one of the town's biggest employers.
He said: "Thank-you for the past 40 years and here's to the next 40."
Essilor recently invested about £500,000 on a new centre of excellence at the site. It was completed at the end of last year, securing jobs and making the most of digital technology, which allows the company to focus on higher value lenses.
The company, which is French in origin and has a global HQ in Paris, has also produced a booklet telling the story of Essilor in Thornbury.
It tells how the search for a new UK base coincided with the opening of a new commercial development in Cooper Road, with production starting in 1974.
Since then, Essilor has experienced two periods when redundancies had to be made.
But Mike Kirkley, managing director of Essilor Ltd, said: "Essilor today is in a very good position. It has grown from very modest beginnings to the number one in the world and that takes a lot of hard work, dedication and belief.
"Today we have many staff who have been with the company for 20 years or more and many more of ten years or more.
"Thornbury is a place where people turn up every day to do the best they can for their company, providing the best service they can to our customers, while creating an environment which is enjoyable and rewarding."