SCREEN CORNER KEY
See our 95-268. Look over the dimensions and see if you think this corner key matches up.
Apologies! I went off your photos and should have read more closely what you said. Your Andersen corner key looks more like our 95-169. Now, note that Andersen made changes to these corner keys in the early nineties; and the older style is no longer available as far as I know. If your key's dimensions don't match what we list for the 95-169, then I'm afraid you might have one of these older, discontinued keys. In that case, you might have to try finding an old millwork that sells Andersen windows; they sometimes have the old-style corners still on replacement screens.