Stitching SPI Calculator
Recommended stitches per inch, thread size, and pricking iron pitch by leather thickness and project.
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Veg-tan leather (shoulder)Hermann Oak and Wickett & Craig are the two domestic tanneries leatherworkers argue over. 4–5 oz for wallets and straps; 8–9 oz for belts and sheaths.
Pricking iron / stitching chiselsJapanese-style chisels (4mm or 3.38mm pitch) produce the tightest saddle stitch. Sinabroks and Crimson Hides make affordable starter sets.
Edge beveler + skiverA #2 edge beveler handles most weights. Seiwa bevelers and Tandy Pro are the reliable options. A skiver lets you thin edges and folds cleanly.
Waxed thread (polyester/linen)Ritza 25 Tiger thread is the standard — polyester with wax coating, strong, consistent diameter. 0.8mm for most work; 0.6mm for fine pieces.
Leather dye + conditionerFiebing's Pro Oil dye is the reliable penetrating dye. Follow with neatsfoot oil or Lexol conditioner. Resolene or Atom Wax for a finish topcoat.