This is a metric module 1 change gear used on Shoptask / Shopmaster machines as well as in most all Chinese and European lathes and other equipment. It has the 4 spline center hole which offers good contact and support, while making it easy to change out for different ratios.
NOTE: The picture is of several different size gears for illustration purposes. You are buying a SINGLE gear. The number of teeth is the last 2 digits of the part #.