These plastic caps keep dirt, debris and animals out of fire department connections, hydrants etc. They are an economical alternative to brass caps. They are not threaded, but simply attach to the inlet's pin lugs using eye bolts (included)and are easily broken with a hydrant/spanner wrench. See item # 09204 for an aluminum version of this item. See item 09205 for a plastic break cap that screws on. Sold in packages of two.
Note: Most FDC's are 2.5", which refers to the diameter of the fire hose, not the diameter of the connection. The outside diameter of these caps is 3.5", the outside diameter of their inner ring is just under 2.75", and the lug connection holes are 4" apart.