The space between characters in a line of type. Letterspacing can be overall or selective. In overall letterspacing, also called tracking, all the letters are affected; in selective letterspacing, more commonly referred to as kerning, only certain letter combinations are affected, such as AT, AV, Te, Yo, LY, etc. The amount of kerning required will depend on a number of factors, such as the specific letter combinations, the typeface, and overall letterspacing. While kerning is now done automatically by typesetting and layout software, with metal type, adding space between letters and words was accomplished mechanically by inserting pieces of metal between the type. This spacing material, being lower than the type itself, did not come in contact with the paper and therefore did not print. For letterspacing, most fonts had spaces of 1 point (made of brass), which could be used singly or in groups. Other spaces were even thinner: 1/2 point (copper) and 1/4 point (stainless steel). There were even letterspaces made of paper, which is how fine adjustments were made. See illustration under tracking.