The red numbers identify each part. Number 1 is a 1/2 inch male adapter. Number 2 is 2 x 1/2 inch bushing. Number 3 is a 2 inch slip cap. The slip cap has been drilled by me to make sprinkler holes for the water streams. The slip cap slides over the bushing and makes a fairly tight fit by itself. You could glue it, but leaving it without glue allows you to remove it later.