For hand leatherwork, use waxed polyester thread matched to the leather weight — 0.55mm for fine small goods such as card holders and slim wallets, 0.65mm for wallet-weight and mid-weight work. Pair with blunt-tipped harness needles (John James L3912 range, size 002 for most work). The thread should fill the pricking iron hole cleanly without needing to be forced through.
For most hand leathercraft, 0.55mm thread suits fine small-goods work — card holders, slim wallets, and key fobs at closer stitch spacing. A 0.65mm thread is the more versatile choice for general stitching on wallet-weight to mid-weight leather. The thread should fill the hole made by the pricking iron cleanly without being forced through it.
Waxed polyester thread is the practical standard for most hand leatherwork — consistent, strong, does not rot, and runs smoothly without additional treatment. Linen thread is the traditional choice with a slightly textured surface and a more organic appearance; it requires waxing before use. Both produce excellent results when used correctly; polyester is the sensible starting point for most makers.