I’ve tried soaking and scrubbing with vinegar a few times but still can’t find any sort of Allen wrench key hole. Although there are still a few holes filled with corrosion so it could be hiding in one of those. How is this supposed to be removed? Thanks!

EDIT: It was 2.5mm hex. I was able to get the cartridge out, but it came out a little weird. Anyone able to take a look at these images and tell me if this is normal? http://imgur.com/a/EEn11T6 I have descriptions for the images. Let me know if they aren't visible.

I think HD67551-1208D2 is the faucet model for my Glacier Bay kitchen faucet. The ID tag only has the "08D2" part readable. According to the manuals I've found online, this model's set screw has part # RP50002. However, even with that number, I still haven't been able to find the hex size.

I'm trying to replace the cartridge/valve stem for the handle, but have been having a tough time figuring out what size/type of key I need. I'm pretty sure it's hex/Allen, but not 100%. But it may also be a security/tamperproof hex.

Here's the best picture I've managed to get of the set screw so far: https://imgur.com/a/iOxQDyQ.