Thread Size And Stitches Per Inch For Hand Stitching

[Avgvstvs]

Good people of the forum, I beseech thy wisdom!

I have been looking for some kind of guideline concerning thread size to stitches per inch ratio for hand stitching. I rummaged around the forums trying to find the info but this thread seems to be as close as it gets:

http://leatherworker.net/forum/index.php?showtopic=53981&hl=%2Bthread+%2Bsize

Now, this is on machine thread. I tried to find equivalents in mm sizes and my understanding is that machine thread sizes are actually mm decimals (207 thread being 0.207mm...?...)* and are quite smaller than those of hand sewing thread. If this is correct, it might be difficult - or impossible (?) - to extrapolate on the above thread's info to make an equivalent for hand sewing...

What thread size/ stitches per inch ratio do you seasoned (and not-so-seasoned) leatherworkers use when it comes to hand stitching?

*I found a chart while googling on the subject but I can't find it anymore. This is from what I remember (poorly) so please don't go too hard on me if I'm wrong.

[Basically Bob]

I stitch at 7 spi with 5 cord/18 linen thread, and I make things like belts, guitar straps, cases etc. . Seems to work good for the things I make. I use Dixon pricking irons to mark the stitches.

[gary]

7 and 8 spi = 0.8mm Ritza thread (that's about 18/3 linen thread).

10 and 12 spi 0.6mm thread.

Dixon pricking irons/wheels.

[Avgvstvs]

This is absolutely false (I can't, for the life of me, find a way to edit my original post...):

my understanding is that machine thread sizes are actually mm decimals (207 thread being 0.207mm...?...)

Thought about it, made no sense, checked it out. Here's something that makes more sense:

"Commercial sizes for heavy-duty thread used in upholstery and webbing (e.g., safety rigging and vehicle tow straps) are 33, 46, 69, 92, 138, 207, 277, 346, 415 and 554. These sizes are the denier measurement divided by 10. (A size 554 thread is about 1/32" or 0.8mm in diameter"

source: http://designer-entrepreneurs.com/blog/illustrations/Thread_Sizes.htm

[Matt S]

It's largely an aesthetic choice. I prefer a slightly chunkier thread to stitch size than is traditional in English work.

A rule of thumb that requires mixing metric and Imperial measurements (in 18-lea based thread) is one yarn per mm between stitches.

e.g. in 5SPI we have 5mm between stitches (a chunky rate not much seen in English work but popular in American style rifle cases etc.) I like a 18/5 linen.

In 7SPI (good for belts and general work on medium-length stitching runs) 18/4 looks good.

In 8SPI (quite fine in American terms but a basic standard in English saddlery) we have 3mm between stitches, and a 18/3 linen thread works well.

As I say I prefer a chunkier thread to stitch size than normal in English style work so I roll my threads from a slightly heavier yarn (12 lea) than the numbers quoted above. Best course (as with most things in leatherwork) is to make yourself a sampler using scraps. Set yourself up some pricked lines in whichever stitching rates you intend to use and try a different thread of each size in each one. Remember to label it, then stick it somewhere you won't lose it and refer to it when making each project for the look you want.