Brief Answer: Normally Variation is there. Detailed Answer: Dear Friend. Welcome to XXXXXXX If you have noticed this for the first time then I must tell you thay this is natural. There can be variation in size and shape of veins of our hand and also difference can be there between veins of both hands. However, if you have pain, redness and swelling over thay area , it might be a sign of thrombophlebitis. So in case you have such problem, it's a matter of concern , else it's a normal thing. Tell me if anything else related to this is troubling you, I will try to help you out. Good Luck.