I've no idea if anyone will read this but we'll see how things develop.
i make leads in a range of widths, the leather thickness (or depth) is a constant at just under 4 mm, but the concern is what width of lead should I use?
If I'm doing obedience training & I have a large, mature dog that is untrained & a bit of a handful then I'd be happier with a wider lead rather than a narrow lead.
If the dog weighs in at somewhere between 30 - 40 kgs then one of my 12 mm leads with a HD clip will hold the dog.
A heavy dog of 40 kgs + that is not well behaved then a 15 mm lead would be my recommendation.
Obedience leads can be made up in whatever length a client wants but as a recommendation, I'd suggest 1.2 m.