Twenty years ago, I did this by buying pre-rolled lace from the hobby store and gluing it onto the halter rings via a short snippet of flat lace. That worked reasonably well, but there were definite color matching issues. I tried to ignore them, but I'm a tack snob--I wanted my halters to be all one color. Eventually I scrapped the short-cut and learned how to roll my own lace.
Here's a look at a full sized rolled throatlatch. The leather strap is folded in half lengthwise and sewn shut. Depending on the type and quality of halter, there will be either a cord or a wire hidden inside the rolled section.
To make a model sized rolled throatlatch, place a nearly completed halter on the model's head. Measure the distance from one halter ring to another, following the line of the horse's cheek.
Cut a piece of 1/8 inch lace, point the ends...
and prepare it with a combination of skiving and sanding. It's important to work slowly and carefully--the finished product will look much better if the lace is of a consistent thickness throughout its length.
It's also important not to over-prepare the leather. Paper thin lace will result in a throatlatch that's flat rather than rounded. You should be able to pinch the leather together just enough to leave a crease down the middle.
Once the leather is ready, flatten it out and apply glue to the flesh (back) side.
Pinch the sides together again and hold until they stick.Hold the throatlatch between your thumb and index finger and roll the throatlatch back and forth until the glue is completely set.
You should now have a nicely rounded throatlatch!
Attach the throatlatch to the halter by threading one end of the lace through the appropriate halter ring.
Add a little dab of glue...and secure in place. The point should fit nicely into the the beginning of the rolled section.
A this point, it's wise to put the halter back on the model and double check the length before proceeding. If your throatlatch is a bit too long (and mine often are!), it may be necessary to shorten the rolled section. Fortunately, this can be done fairly easily using the tip of an awl.
The finished project.
Questions, comments or suggestions for future Tack Tip tutorials--please post them to the comments section!