Nipples and saddles

[Shells]

I'm just about to start building a nipple PVC pipe water system for my hens. I notice that the company I am going to buy the nipples through also sell "saddles" with them if wanted to fit two different sized pipes. Can anyone tell me what they are for? are they to be used with the nipple somehow or are they to block an unwanted hole?

 

[MR.PEEPS]

can you send the link to the site and I sell the nipples I dont know what there price is but mine are $1 each I have a listing in the buy sell page.