Learn how to connect pieces of chainmail. Some of them are best understood by reading the previous chapter Expanding & Contracting.
The Gusset Seam consists of a bunch of expansions aligned in a line. That line stands perpendicular to the rows in the mail. The Gusset Seam can be created by connecting triangle pieces with rectangular mail. Such triangle pieces are called gussets in reference to medieval textile tailoring. Gussets help to widen a garment like a skirt.
The Merging-Rows Seam is eliminating rows. At the end of each eliminated row, there is either a gap or a ring holding less than four neighbors. The Merging-Rows Seam seam is generally used to taper sleeves.
The Cross-Grain Seam connects pieces of chainmail at a 90° angle. One piece has rows running along the seam. The other piece has rows running perpendicular to the seam. Between the pieces, there is a line of rings that is a mix of both mail orientations. Its rings are holding four neighbors each. Yet there is some space between them. This seam is typically used for a short horizontal line in the armpit.
The Turn Seam also connects two pieces of chainmail in a 90° angle. Both pieces have rows running at a 45° angle towards the seam. This is turning the whole pattern while maintaining the regular 4in1 rings order in all places. There are no rings holding less or more than four neighbors. Thus the Turn Seam helps to keep gaps minimal.