On October 25, 2012, Russ Sharples in New Jersey, USA wrote:
"There's a shot of my windscreen glass - Royal Doulton. It was in the car when I bought it. Using a crude caliper it measures 0.216 inches thick".

All mention I can find about Royal Doulton windscreens on the internet refer to 20-50 years ago, so I recon this is not much use today. One note claims, "Avante screens were made by Royal Doulton, who sold their windscreen division to Pilkington". So it stands to reason that the Royal Doulton source is long gone.