Hibbent 10-Piece Faucet Aerator Key Set - M16.5 M18.5 M21.5 M22.5 M24 Aerator Wrench Tool with Ring for Easy Storage - Perfect for Kitchen & Bathroom Faucet Maintenance (2-Pack)

I recently installed a new Delta faucet in my bathroom and before I got the project finished, the box containing the aerator key got thrown away. Luckily, the instructions weren’t in the box. The Delta instructions showed a Neoperl aerator key. So at first I considered buy a set of them. I looked up my part number (RP91142-1.2) and from a Delta faucet answer on Amazon for an aerator they said the size was M18. This had me confused because I couldn’t find any keys that were M18. They were M18.5I also measured across what I thought was the diameter of the aerator (0.72”). I did the calculations to figure the MM, multiplying by 25.4, and I figured my aerator was a size M18.5.However, I got looking at some other reviews where the commenters talked about Delta bathroom faucets and the size of their aerators. And those comments said that the size was the smallest (M16.5). Well, the Neoperl sets I looked at only had 4 keys. Their smallest key was M18.5. I got thinking, “What if the size of mine is actually M16.5?” So I decided to buy this set instead.I’m glad that I did. I tried the next to smallest key (M18.5). It didn’t fit. I thought... UH-OH...NOT GOOD! I thought maybe the teeth size were off such as too wide or something. Then I tried the smallest key (M16.5). The key fit!The diameter is a little smaller than it looks. If you’re going to buy a set of aerator keys for a Delta bathroom faucet and you think your size is M18.5, get a set that includes the M16.5 to remove it just in case.Getting a set with 5 keys saved me from wasting time and money by having the right key instead of buying a set of 4 keys that had every key except for the one I needed.This set seems a little thin, but I think it is plenty strong enough to remove the aerator. It removed mine just fine, although my faucet was brand new.It’s nice having four sets of 5. It cost me only a dollar more than 1 set. So if one set breaks, no big deal. I threw a set under the sink cabinet to leave it there. That way in case I ever need it, I have it handy. I’ll likely stick another set in each of my toolboxes.There’s probably only two minor complaints:1. It would be nice to have a different shaped key ring or bigger key ring so it is a little easier to use the key while on the ring.2. The sizes aren’t marked. This isn’t a big deal, but it would help. Just grab a sharpie and mark it on them.