Mm To Spi For Pricking Irons

[Glendon]

Hi all,

Could someone give me a quick millimeter to stich per inch conversion for pricking irons / diamond stitching chisels? For a while now I have been using lacing chisels to make stitching holes. I gave up on the overstitch wheel pretty quick. I think its about time I pick up some proper stitching chisels though. Most of the ones I’m looking at are from the UK or Japan, and I can’t quite work out how the teeth sizing in mm converts to stitch per inch without holding a tool in my hand.

[Effuse]

Seiwa & Kyoshin Elle

These pricking irons are measured as the distance between the points i.e. The stitch length.

They don't use a width for the iron, they use a number of prongs (1, 2, 3, 4 or 6).

These are expressed as a x b mm on the store, so 3.5mm means 3 prongs with 5 mm stitches etc.

The stitches per inch = 25.4 / stitch length:

• 3mm ~= 8.5 stitches per inch
• 4mm ~= 6.3 stitches per inch
• 5mm ~= 5 stitches per inch
• 6mm ~= 4.2 stitches per inch

Craft Sha

The Craft Sha irons are measured as the distance between the prongs. these are half the distance of the ones above, so

• 1.5mm ~= 8.5 stitches per inch
• 2mm ~= 6.3 stitches per inch
• 2.5mm ~= 5 stitches per inch
• 3mm ~= 4.2 stitches per inch

Again with the Craft Sha the first number is the number of prongs, so 10x1.5mm means 10 prongs giving 8.5 stitches per inch.

These numbers are not my own, ALL Credit goes to Ian Atkinson for doing the leg work, I have simply transcribed the work he's done here.

[Glendon]

Thanks so much for taking the time to repost this over here. It was really helpful. I follow a lot of Ian;s work. I guess I don't check his site quite enough since I missed this info.

[RavenAus]

Thanks from me also My local shop has the chisels in mm and the stitch markers in spi so it's really helpful to see this.

[pgivens]

I just posted this in a thread about the new Tandy Fine Diamond chisels, but it seems more appropriate here...

The sizing on the Tandy diamond chisels refers to the size of the prong, not the space between prongs. The spacing is as follows:

STANDARD DIAMOND CHISELS:

• 4mm - 4 stitches per inch
  
• 3mm - 5 stitches per inch
  
• 2mm - 6 stitches per inch
  

FINE DIAMOND CHISELS:

• 3.5mm - 7 stitches per inch
  
• 3mm - 8 stitches per inch
  
• 2.5mm - 9 stitches per inch
  

[skylerbarger]

What's the difference between the diamond and European style pricking irons? Pardon the ignorance.

[billybopp]

Both are to help you mark exact spacing for your stitches when hand sewing leather.

Diamond punches or chisels are meant to poke holes all the way through the leather so that you don't necessarily need to use an awl to open up the hole to sew. The holes are diamond shaped .. hence the name.

"European" pricking irons only make a narrow angled slit in the leather that you then further open with an awl before sewing. something like this ... / / / /

Hope that helps

Bill