>Can't check from where I am now, but the 4027 has 10 pins. I think the >4017 has fewer. My 4017s have 12 pins and the 4027s less. I have different 4027s. Some are encapsulated and some aren't. My earliest 2600 has a 4027 in place of a failed 4017 so I know that works just fine. -Cary