San Francisco (CNN Business) In the nearly four years since Microsoft introduced its HoloLens augmented-reality headset, consumers have largely forgotten about it. But now it's gaining traction among an unlikely audience: car makers.

Toyota is one of a growing number of auto makers hoping augmented-reality headsets can improve everything from designing cars to manufacturing and fixing them. These headsets let users merge 3-D images with the real world.

For example, Ford and heavy-duty truck maker Paccar are among those using the HoloLens to help design cars, and Daimler recently said it purchased over 100 HoloLens headsets to train its mechanics with 3-D models of vehicles and parts like brake systems.

But the augmented-reality market is still small: Eric Abbruzzese, an augmented- and virtual-reality analyst with ABI Research, expects more than 2 million headsets and smart glasses will ship this year. Most of that market is made up of businesses still testing the technology. Abbruzzese predicts it will grow to 29 million by 2023.

The most recent example of car makers adopting the technology is Toyota. At its headquarters in Japan's Aichi prefecture, employees like Koichi Kayano are experimenting with HoloLens for a variety of tasks. Kayano, a project manager who finds ways to use 3-D models across the company, is using the headset to speed up the process of measuring the thickness of a vehicle's paint and rust-prevention coatings to ensure consistent color and avoid corrosion.

Read More