Scabbard chisels (also known as saya nomi or saya chisels) are bent handled, bull-nose chisels used by Japanese scabbard makers.  But these hand forged chisels can be used for a host of other wood-working and knife making tasks.  Any sort of shallow channel can be easily chiselled out with a saya chisel.  The chisels feature hand turned handles in a variety of woods, and the roughly 1 cm (.4 - .5 inch wide) blades are forged from W1 high carbon steel.  Each chisel is uniquely finished, slightly different in size, and bears some of the marks of forging.  No two are alike.  See the Youtube video from 5/5/23 for more details. 
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