平ひら歯は車ぐるま

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Meanings

1

noun

spur gear

A gear with straight teeth parallel to the axis, used to transmit motion between parallel shafts. Technical term in mechanical engineering.

even, flat, peace

歯tooth, cog

はすば歯は車ぐるま
Helical gear; teeth are cut at an angle, providing smoother and quieter operation than spur gears.
かさ歯は車ぐるま
Bevel gear; used to transmit motion between intersecting shafts, unlike spur gears which work with parallel shafts.

Compound of 平 (hira, 'flat') + 歯車 (haguruma, 'gear'), referring to the flat, straight teeth of this gear type.