You all gave me a big laugh with this discussion! And the title!!
When you purchase a clasp, at least from companies like Stuller or Rio, they give the length of the clasp. Really helpful when the finished length of a necklace needs to be at least 18 inches, given 16 inches of unstrung pearls. I figure about 1mm per knot, with 25-30 knots being about 1 inch of added length or 25mm. These would be large pearls, for example. Gimp will add about 2-3mm also.
We are pretty much stuck with adjusting the thread size to whatever size the pearl drill hole is, and that requires experimentation for me also. Of course, we could be like JP and drill our own pearls!
I usually slide the needle on the uncut end of the thread, double it and see if it goes through the pearl and doubles back with no problem. Sometimes I test a few knots also.
Sunseeker, your rope turned out beautiful! I've been wanting something similar, as most of my necklaces are one color and about 20 inches.
It's pretty much a personal thing how each feels about the size of knots vs size of pearls.
You may have heard of Paspaley's invisible knotting. Their SSP are strung very tightly and the knots between don't show. It makes the necklace very stiff. I was able to examine Pearly Shell's at Ruckus and was unable to figure out how the heck they do it! This technique would only work for a short necklace, not a rope. I hope someday one of us will be asked to restring a Paspaley and find out their secret!
Many thanks to each of you, Sunseeker, Karman, BWeaves, Marianne, P-W, Amti, Hanadama, Katbran, JP for sharing your experiences working with Beader's Secret thread and supplies. I feel like being able to knot the pearls we love to wear and gift to loved ones is icing on the cake!