These are the guttural Devanagari letters:
The guttural consonants are from the first line of the consonant system in Devanagari. They come first because they are produced the furthest back in the throat-mouth system.
Guttural is derived from the Latin word for throat “gula” and means as such “from the throat”. The term describes the fact that the sounds are produced in the throat. In Nepali those sounds are produced at the top of the throat (where it connects with the mouth space). Therefore the Nepali guttural sounds do not sound as harsh as other guttural languages as for example German or Semitic languages (Arabic (especially the eastern versions), Hebrew).
The Devanagari the guttural letters (as well the retroflex, palatal, dental and labial) are organized as such:
Non-sounding, nonaspirated : क
Non-sounding, aspirated: ख
Sounding, non-aspirated: ग
Sounding, aspirated: घ
Here I explain the writing in detail: