These C.H. Hanson 21 in. Blue Marking Flags are ideal for surveying, construction and agriculture. These durable, long-lasting marking flags are constructed from weatherproof poly vinyl chloride that is designed with toughness to hold up to harsh outdoor conditions and maintain its shape. The marking flags are high visibility, fade resistant flags that easily mark communication, alarm, or signal lines. Get the job done right with these marking flags! Mark the location of underground sprinklers, pipes, and lines with these marking flags!