Please help me identify pfister part

[pstohlty]

For the pfister shower cartridge, there is a groove on the bottom that slides onto a black piece in the wall.

When I was changing the cartridge, said black piece came loose and fell into the wall. Now, the entire cartridge is sticking out of the wall. I need help identifying the piece and knowing where I can buy it. Thanks!

 

[pstohlty]

For the pfister shower cartridge, there is a groove on the bottom that slides onto a black piece in the wall.

When I was changing the cartridge, said black piece came loose and fell into the wall. Now, the entire cartridge is sticking out of the wall. I need help identifying the piece and knowing where I can buy it. Thanks!

 

[Sponsor]

 

[pstohlty]

First photo is how it looks now (without the black piece). Notice how it’s sticking out. Second photo has the black piece and notice how it’s sitting in the cutout
Photos

 

[Marlinman]

No photos. Does it look like any of these? Some cartridges have had a color change.

 

[pstohlty]

No photos. Does it look like any of these? Some cartridges have had a color change.
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I tried uploading some photos in my reply. But I am looking for what the cartridge groove should slide on to hold the valve in place in the wall.