An ith rune is a low tier rune that can be socketed into armor and weapons. You can cube 3 eth runes together to get an ith rune. You can also obtain an ith rune from normal countess. You can get an ith rune from the normal hellforge quest.
An ith rune requires level 15 to use.
Horadric cube recipes with ith runes
transmute 3 ith runes to create a tal rune