"A Well moderated board that is a benevolent dictatorship, not a democracy" In business since June 16, 2010
My guess is the metric set has 17mm and stops at 19mm.That they would fill the gaps with having both sets like a lot of homeowner grade sets do.In the metric set 11, 15, 16, 18 mm would be the possible gaps.
The Industrial set also included 20mm -- which is a size I don't recall I've ever used.
Yep, 11/16" not popular for cars, hugely popular on tractors.