From Reddit, a list of the thinnest Apple devices:
- iPod Nano 7th gen – 5.4mm thick
- iPad Pro 2018 – 5.9 mm
- iPod Touch 5/6th gen – 6.1 mm
- iPad Air 2 – 6.1 mm
- iPad Pro 10.5inch 2017 – 6.1 mm
- iPad mini – 6.1 mm
- iPhone 6 – 6.9mm (thinnest iphone)
If accurate, this makes the new iPad Pro the second thinnest device Apple has ever made.