This loom requires several small bobbins.
The common loanword for 'bobbin' in modern Japanese; へそ is a native Japanese term that is now rare and mostly found in traditional crafts contexts.
A more general and common word for 'spool' or 'thread winder'; へそ is more specific to traditional bobbins.
Rare kanji spelling for 'bobbin/reel'; the reading へそ is not obvious from the characters.
Alternate rare kanji spelling; 綜 relates to weaving and 麻 means hemp, suggesting a traditional association.
The origin is uncertain. The kanji spellings 巻子 (literally 'winding child') and 綜麻 (hemp weaving) are likely ateji or conventional associations rather than reflecting a clear historical derivation.