Van Heusen short sleeve regular fit shirt.  Neck 16.5.  Pit to pit is approx 24 inches.

NOTE - the label in the collar has been cut.  Missing some of the original packaging so listing as used although it still has some pins in the neck and some packaging and may just have been on display.
(Small Mark noted and pointed out in 2 pics)
If you have any questions please ask and thanks for looking!