noun
helical gear
A gear with teeth cut at an angle to the axis, used in machinery for smoother and quieter operation than spur gears.
この機械には斜歯歯車が使われている。
This machine uses a helical gear.
平歯車 is a spur gear with straight teeth, while 斜歯歯車 has angled teeth for smoother engagement.
Compound of 斜 (hasu, 'diagonal') + 歯 (ha, 'tooth') + 歯車 (haguruma, 'gear'). The reading はすば is from 斜歯 (hasuba, 'oblique tooth').