This section is from the book "School Needlework. A Course of Study in Sewing designed for use in Schools", by Olive C. Hapgood. Also available from Amazon: School Needlework: A Course Of Study In Sewing Designed For Use In Schools.
In the manufacture of cloth-covered buttons, two round pieces of cloth, one for the covering and one for the shank, two collets of tin and a thick paper filling are used. The tuft of strong linen is placed in the under collet, and a die or stamp comes down, and presses the tuft through the collet, making the flexible shank by which the button is sewed on. The cloth covering is then placed on the upper collet or shell, and pressed up into a die. Just before the die holding the upper part of the button is pressed into the one holding the under part, the paper filling is put in. As the dies come together they turn the edge of the shell over the collet, and the different parts are thus held strongly together.