double-pointed nail; dowel
A nail or pin with points at both ends, used to join two pieces of wood together; also refers to a dowel used in joinery.
I joined the two boards firmly with a double-pointed nail.
This piece of furniture is assembled using dowels.
Standard kanji spelling.
Variant without the okurigana い.
Uncommon variant using 間.
Mixed kanji-kana spelling.
Mixed kanji-kana spelling without okurigana.
Compound of 合い (ai, 'joining') + 釘 (kugi, 'nail'). The spelling 間釘 uses 間 (ai, 'space, interval') for the same reading.