Horns.7z -
Place .hak files into the /hak/ folder and .erf files into the /erf/ folder.
To provide more specific instructions, could you clarify or what game/software you intend to use it with? Carved Horns 7Z/061 - Archive Fifty-Five Horns.7z
The native tool for this format. You can download it for free from the official 7-Zip website . Horns.7z