Young guys at the auto parts store

OK, funny story. It's funny because I'm the dumb ***.
I'm in a hurry and getting plugs for a 440.
I run to the story and say they are all the same and make up a car.
Get home and the plugs have a gasket. They won't go in the engine.
The hole in the head looks funny but I'm rushing and it didn't register to me.
I'm thinking the computer system is screwed up.
I made two trips to Autozone and one trip to O'R before it dawned on me.
It's a motor home 440 and there might be a difference.
A few minutes online looking for chatter in a car forum. Yep. Different.
Damn it's a tapered seat plug.
What's that, Chevy?