Socks specifications of needles. Generally, there are 120 needle, 144 needle, 168 needle, 200 needle. 96 needle and 72 needle are very seldom to use, there’s no much demand and most machines are not computerized, which mainly for producing the thick needle socks; 220 needle mainly to produce high end sock which has high requirement for the material like mercerized wool. Now we only introduce the difference between 144, 168 and 200 needle which commonly used.
The following picture is a sock machine:


Socks, are mainly produced by 144, 168 and 200 needle, needle means the needle quantities inside the hosiery machine, 144 needle means there are 144 needle for one loop, because the diameter of the cylinder is fixed, so the greater the number of needle, the weaving more dense of the sock.
The following picture is the 144 needle with half terry/cushion socks, 144 needle normally used 3 ends of yarn so it is the thickest socks, mainly used in sports /athletic socks.
168 needles are mainly double yarn socks, which is slightly thicker than 200 needle, mainly used in normal casual socks, crew socks, mid-calf socks, and knee socks.

from yeleosocks.com