This is the most common type of keying for residential applications. It refers to a non-interchangeable core setup.

Commonly called "BEST prep". Looks like a small figure 8 cutout and is consistent across most manufacturers, meaning there is only one size.

Newly manufactured items are setup for both 6 or 7 pin cylinder lengths (this did not used to be the case). 6 or 7 pins only needs to be specified if you are ordering a core now.

Note: A spacer can be used to put a 6 pin core into a 7 pin housing.

Different manufactures make their own sizes. The backside of the cylinder also changes so they lock in differently.

Corbin, Sargent, Schlage, KABA, and Yale each have their own size and version. See examples below.