The LG X screen spotted in FCC filling carries model number K500n, and it was certified by GFC (Global Certification forum) too on March 16.
According to the FCC documents, The LG X screen K500n model supports GSM 850/1900, LTE band 4 and Band 5.
LG X Screen Key Specs:
X screen Key Specifications:*
Display: Main) 4.93-inch HD In-cell Touch
Secondary) 1.76-inch LCD (520 x 80)
Chipset: 1.2GHz Quad-Core
Camera: Rear 13MP / Front 8MP
Memory: 2GB RAM / 16GB ROM
Operating System: Android 6.0 Marshmallow
Size: 142.6 x 71.8 x 7.1mm
Colors: Black / White / Pink Gold
By the way, The South Korea version of the X screen comes with model number LG-F650K,LG-F650L and LG-F650S.
Source: GCF http://www.globalcertificationforum.org/devices/certified-devices/5590.html?view=terminal