For pens, brushes, glasses, and similar items. Often written in kana.
Rare architectural or historical use for an enclosing structure or outer fence.
The outer fence of the old castle remains.
The samurai put his sword back into its sheath.
I lost the cap of my fountain pen.
The spread on this trade is small.
He profited from the price gap between the two markets.
He drew the sword from its sheath and took a stance.
Lately the spread between the two stocks has been widening.
Used because 鞘 (saya, a sheath) is a long, slender object, which is naturally counted with 本 (hon).
margin; spread
red-lacquered sword sheath
outer roofed structure for protecting cultural assets and historic sites
tip of a scabbard
spear squid
Standard kanji spelling for scabbard, sheath, and related meanings.
Kana spelling is common for the cap/case/sleeve sense and the financial margin sense.
Katakana spelling is sometimes used in financial contexts for the margin/spread sense.
The origin is uncertain. The kanji 鞘 is conventionally used for scabbard and sheath, and by extension for other enclosing objects.