Charging cable

Apple cables may vary slightly by geographic region - and by time. Presumably, in common with many manufacturers, cables will be manufactured by third-party suppliers to a defined electrical specification. As such, different suppliers may use cables that vary, slightly, in physical dimensions.

The overall jacket dimensions are largely of no relevance or importance - the USB-C connectors being significantly larger than the cable.

That said, the standard USB-C to USB-C 1m cable, supplied with a recently obtained iPad Pro 12.9, is ~3.0mm. The optional 2m USB-C cable is slightly larger at ~3.5mm diameter.

Hello ~ Take a look here as well:

Power & Cables - iPad Accessories - Apple

~Katana-San~

You mean length of the charging cable?

Hello ~ Take a look here and they are available in different lengths as well:

Lightning to USB Cable (0.5 m) - Apple

~Katana-San~

Lightning connecter is standard for all apple devices

I don't believe the diameter of the cable is a published specification.