These are picture examples of parts.  If asked to go buy

 

This is the most common valve you will find under the sink or toilet.

What to tell the floor person you need:

• The size will be either 1/2 inch or 1inch and the twist of the turn.
• Type Screw on, Solder or Shark bite.
• All are copper but have been chromed.
• See below for more examples of parts

 

 

 

 

See Below