I think it is unfortunate that we use the term "zipper foot" to identify the sewing machine presser foot that has one or the other toe removed to enable a stitch right next to an object. It is true that such feet can and should be used with the very small zippers that are encountered in dressmaking, but the zippers that we use in canvas work are quite large. Nothing is gained here by the use of the half size foot. Indeed, feeding capacity and stitch quality will be degraded if such feet are used.

Where then do we use zipper feet? The most common application is to install the "sticking stitch" right behind a boltrope in a sleeve along the luff and foot of a mainsail or along the luff of a headsail. This stitch closes the sleeve right behind the rope. It does not lock the rope to the sail (it will still stretch in the sleeve), but it does tend to cut down abrasion as the rope slides up and down the slot in the mast or boom and it tends to encourage a more even "gathering" of the cloth on these roped edges when halyards are eased to increase draft in light air.

Zipper feet are also used to make and install welting. Welting, by the way is a bead of cord in a fabric sleeve or a prefabricated plastic extrusion (with the cross shape of a tadpole) that is sandwiched in a seam (usually on a cushion) as trim.There are, however, special presser feet with tunnels for installing welting. These feet are optional for our bigger machines. The Ultrafeeds have welting tunnels built into their standard walking foot. So zipper feet are used with welting only if a better option is not available.

One final comment. If the zipper foot leaves the needle "unprotected" on one side, that is, if metal does not completely surround the needle, there will be a tendency for stitch tension to vary depending upon the angle of the fabric on that side of the foot. That is why I mentioned that stitch quality could be degraded by the use of a zipper foot above. The Ultrafeed walking foot mechanism does not suffer from this problem but, as a consequence, it is not possible to get as close to an object as would otherwise be possible.

The right hand zipper foot on a Sailmaker machine. This is a "staged" shot (the stitch was done earlier), but you can see how close the needle is to the boltrope.		Another "staged" shot of the left hand zipper foot on the Ultrafeed LSZ1. Note that the needle bar has been moved to the far left in its slot, but there is still a bit more distance between the needle and the boltrope because of the closed inner foot. I have ground away the inner foot on my own personal Ultrafeed machine until just a sliver of metal remains on the right side to make possible a better "sticking" stitch for boltropes -- this same inner foot can still be used with the normal walking presser foot.