Most parts and pieces are modified parts from females…. So the ball sack is the same as vaginal lips anatomically speaking. But to have a ftm transition you generally need to get a hysterectomy. They fashion the penis using skin from your forearm or thigh, and use the labia to make the ballsack… I’m not an expert but I did just do some research online. The photos are not the prettiest in the world so nsfw on that but it is pretty interesting and they do a pretty good job. It looks like penis’ and vaginas.