The basic type 4-thread overlock machine is equipped with the special gauge sets to realize condensed and beautiful stitch and then flattening the stitch by hand or by flattening machine (OSF-100) to make the butted seaming.
Standard looper for 3-thread and spreading looper for 2-thread.
The stitch width is 3mm or 5mm for optional.
(It can be converted to basic 4-thread overlock with standard gauge set.)