These adjustable 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 have an adjustable bar that, once adjusted for diameter using the screw and bolt, threads onto any hose thread. They are easily broken with a hydrant/spanner wrench. See item 09207 for plastic break caps that over the inlet's pin lugs. SOLD INDIVIDUALLY.
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 this red plastic cover is 3-5/8", and the metal bar on the inside adjusts from 2-3/4 to 3-5/8" (to match the inner diameter of your female connection).