Compartments also held spacers, which are blocks of blank type used to separate words and fill out a line of type, such as "em" and "en" quads ("quadrats", or spaces. A "quadrat" is a block of type whose face is lower than the printing letters so that it does not itself print.). An em space was the width of a capital letter "M" – as wide as it was high – while an en space referred to a space half the width of its height (usually the dimensions for a capital "N").