"When Trapp wants to change it up he goes with his stock 1969 Gibson ES-335 w/ trapeze tailpiece. Both guitars are strung with D’Addario NYXL .010–.046 strings."
-Premier Guitar; Rig Rundown with Guthrie Trapp
"I've used D'Addario strings since I started playing guitar. 10's to be specific, but occasionally I'll use 9's."
Taken from this interview: http://www.truthinshredding.com/2013/05/nick-johnston-cosmic-interview-with.html