Is It Normal To Have Thick Veins On The Testicles?

I am 21 years old and the tube running out of my left testicle is much thicker than my right. I have a child that was conceived 5 years ago. During a testicular self check I noticed it was noticably thicker. I have no lumps or pain in my testicles. Also the veins seem to show more on the outside of my scrotom on the left side than the right