Question on a carburetor

[84chevyguyid]

I am doing a carb kit on a 76 chevy with a 350 in it. I dont recognize what this piece is in the body of the carb. I pulled on it a little but it doesnt want to come out. Do I need to remove it or should I leave it alone?

[geezer#99]

That's your APT. Adjustable Part Throttle.
Controls how deep your metering rods go into the jets.
It screws in. Leave it in, it won't hurt anything.
If you do remove it make sure you count the number of turns so yo can put it back exactly as found.