Most Likely Not A 19mm Nut, Thats The Wrench Size Used To Take It Off, (if Its Like An Srx ) The Threaded Shaft Is Not A 19 Mm , Its Smaller Cause The Wrench Needed To Take Off The Nut Is A 19mm.
***for Example A 1/4 Inch Bolt Needs A 7/16 Wrench.5/16 Needs A 1/2 Wrench ***
From What I Can See Its A 14mm * 1.5 (used My Wrench As To Gauge The Thread Shaft Diameter) And The 1.5 Is The Thread Pitch Using My Thread Gauge With My Tap Set. I Hope This Helps. Hopefully Its Right. Got A Fastenal Store Around There , There Always Good At That Stuff.