How the part fits? 1-5/8" rail end has the inside diameter of 1-5/8". It fits over 1-5/8" O.D. top rail.
Where is it installed? 1-5/8" Rail end is installed at the end of the top rail. You will need a rail end at every point of termination.
How many do you need? For every stretch of chain link fence, from terminal post to terminal post you will need (2) 1-5/8" rail ends.