Usually a Carter carb had a viton tipped needle(it feels like a rubber tip) and a brass receiver that the needle lives in, and is threaded into the carb body. Some early carbs used only a metal needle with a brass seat. Other manufactures as mentioned, used a metal or aluminum needle but the brass receiver/seat where the needle lives used a neoprene or viton sealing seat that looked like a disc or "O" ring that the needle seated in, still others had the needle seat pushed into the carb base and some were not replaceable.
Back in the day pre 60's, it was common in most carbs for a needle to be steel and the seat/receiver it lives in, was brass and screwed into the body. With the advent of the viton tip needle, better sealing was accomplished and less fuel leaking into the carb/engine both during operation and storage.
Hope this helps.
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