Which instrument is sometimes used by a symphony orchestra to set the pitch for the other instruments in the orchestra?

The instrument that you're referring to is the OBOE.

Oboes are a family of double reed woodwind instruments. The most common ones plays in the treble or soprano range. They are usually made of wood, but there are some made from synthetic materials.

It is more of a 2 foot long black cylinder with metal keys covering its holes, and its mouthpiece uses a double reed, which vibrates when you blow through it. This makes the oboe, officially, one of the most difficult instruments to play.

Obie are commonly used to tune percussion instruments and all other sections of the band.