Plastic 1 inch BSP cap (blank nut) and washer, use to blank off unused washing machine or dishwasher waste connection (usually on the side of a P trap, under your kitchen sink).
Although this is called a 1 inch cap, it DOES NOT measure 1 inch with a ruler (see pics).
It's NOT the size you need to blank off an unused washing machine water supply, that's usually 3/4 inch BSP (also in our store).
BSP (British Standard Pipe Thread) sizes don’t match up with what you would measure using a ruler. Have a look at the BSPT link at the bottom of this page for more information about how plumbing threads are measured.