Still confused

I am starting to knit on circulars. I have the Needlemaster kit. I have asked this question before and searched the forums but still don’t quite understand. Let’s say I have a pattern the says I need 16in circulars 10 1/2 needles. I know I use the 10.5 needles and this might sound like a silly question, but with that will I use the 12in cable or the actual 16in cable. I only ask this because I know that previously I have been told that I take into account the length of the needles also when determining what circular to use. So if that is the case, for this pattern, I would want to use the shorter cable. Help I am so confused I am having a hard time wrapping my brain around (’:wall:’) not using the actual cable measurement when the pattern states use circulars. Thanks in advance for your help.

the length is tip to tip no matter the pattern…alllllways tip to tip. Unfortunately, you can’t make a 16 inch circ on the needlemaster kit. they don’t have a cord that is short enough for it. you can get an extra set of points and use two of the longer cables to do circular on two circs…and i have heard you can do magic loop (but i think the cord is too stiff for that) but no 16 inch circs in that kit…sorry.