Grover and Baker two-thread chain-stitch sewing machine, 1871.

The double-thread chain-stitch was invented by William O Grover, and in 1851, along with his partner William E Baker, he took out a patent for a machine that would sew with this stitch. This machine is an improved version of the original 1851 model and made a secure chain-stitch. It makes a bulky seam and uses a lot of thread but has the advantage of not having a bobbin to wind as both threads are carried on reels. It was manufactured until 1875 and in total about half a million machines were built.