Buttonholer

A buttonholer is an attachment for a sewing machine which automates the side-to-side and forwards-and-backwards motions involved in sewing a buttonhole.
Most modern sewing machines have this function built in, but many older machines do not, and straight stitch machines cannot sew a zigzag stitch with which buttonholes are constructed. A buttonholer attachment can create buttonholes from any sewing machine capable of making a lock stitch. (That is not to say, however, that some "industrial buttonhole machines" cannot employ a chain stitch, especially to create the "purl" when making "keyhole buttonholes"). 
The buttonholer's adaptor attaches to the machine's presser bar, replacing the presser foot. In its place the buttonholer employs a cloth clamp with teeth on the underside to hold the material firmly whilst manipulating the cloth side to side and forwards and backwards. Driven by the up and down stitching motion of the needle bar via the fork arm straddling the needle clamp, it executes the series of movements to complete a buttonhole by moving the "material" rather than by moving the "needle" position. Buttonholers usually include a metal feed cover plate to cover the machine's feed dogs, so that they do not interfere with that of the buttonholer, though some machines allow the feed dogs to be disengaged or 'dropped'.
Singer buttonholers.
The Singer Manufacturing Company, (often abbreviated by Singer as Simanco), contracted several manufactures to produce buttonholers branded as Singer, in an evolving series of buttonholers that fit Singer machines. The Peerless Buttonholer for use on Singer VS machines was patented in 1887 and made by The Sackett Mf'g Co . The Lenox ' "Famous" Buttonhole Worker' was patented in 1916 (Simanco No. 36935).
Later buttonholer models made for Singer by 'Greist Mfg. Co.' employed templates to create a variety of different buttonhole sizes and shapes including keyhole buttonholes, as well as straight buttonholes, and even an eyelet. Produced for Singer from 1948 into the late 1980s, the Greist template design of buttonholers became Singer's longest running style of buttonholer.
Singer's line of buttonholers includes:-
"'Vertical Needle' when used by Singer to refer to domestic machines, became Singer's modern term for a 'low shank'."
The Simanco Nos. and sizes for the five templates included with the Singer (Greist design) buttonholer kit are as follows:-
The individual Simanco Nos. for the additional four templates not supplied with the Greist design attachment, as well as the eyelet template are as follows:-
The width of the Eyelet varies depending on the setting chosen from narrow to wide. This is also the size of the eye of the Keyhole buttonholes, which likewise depends on the width chosen.
Greist often included a "bonus" in the form of a plastic pouch containing a set of the four additional templates — "usually in grey plastic" — not normally included with the buttonholer, viz sizes:- 3/8" (10mm) Straight, 1/2" (13mm) Straight, 15/16" (24mm) Straight, and a 5/8" (16mm) Keyhole. However, Greist continued to "sell" the Eyelet — made of metal alloy — individually, as well as "selling" templates in a Five-Pack of metal alloy inclusive of the eyelet; and in later years sold an Eight-Pack of templates — that included an Eyelet template — but "only ever made of a black plastic fibre composite", or included them with the purchase of a Greist Buttonholer.
The three new additional sizes offered were:- 1" (25mm) straight, 7/8" (22mm) straight, and 7/8" (22mm) keyhole.
White buttonholers.
Greist Mfg Co. produced a buttonholer adapted to fit White Sewing Machine Company models, and which is internally identical to ones it produced as the Singer 160506 and 160743, or later 489500 and 489510 template-driven buttonholers. Under contract to White, the attachment was branded the 'White Magic Key Buttonhole Worker'.
YS Star buttonholers.
YS Star is a Japanese brand of sewing accessories made by the Yoshikoshi Manufacturing Company since 1945. The YS-4454 and YS-4455 look very similar to the Famous Buttonhole Worker 121704 and 36935, which were patented in 1916 . Three different models are offered, two of which have been cloned by Chinese manufacturers. The Japanese Yoshikoshi buttonholer shows "YS STAR", the star trademark, and "Made in Japan" in various locations.
On all models, adjustment wheels or winged screws set the buttonhole length, 'bight' (zigzag stitch width), and stitch length.