What stem for giant defy?

[Kcyclist]

Looking to lengthen stem from 100mm to 110m on my 2016 giant defy 2 Road bike frame size medium. I'm 178.5cm tall.
Bike is pretty good fit but would like to stretch it slightly.
Anyone recommend a suitable stem? Not sure what to get in terms of steerer / handlebar size etc.

Many thanks

 

[vickster]

Probably an Oversize 31.8mm
Measure the bars?

 

[Kcyclist]

Measured, estimate 31.8mm.
Will go for that size. Cheers 👍