Bull gear

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The term bull gear is used to refer to the larger of two spur gears that are in engagement in any machine. The smaller gear is usually referred to as a pinion.

[edit] Lathe

On a lathe a "bull gear" is a gear which allows one to connect the spindle to the drive shaft. On a South Bend lathe this can be done by engaging a pin which connects the gear to the v-belt pulley or by engaging the back gear.

[edit] Space Station

On the International Space Station, a "bull gear" is one of two large race rings present in each Solar Alpha Rotary Joint which in combination with the Drive Lock Assembly that contains a pinion gear, allows the outer Integrated Truss Structure segments to rotate and track the sun.