Personalized Mechanical Christmas Tree Youth T-Shirt. A Christmas tree made of red and green mechanical gears is a humorous holiday design to tickle the funny bone of your favorite mechanic or mechanical engineer any time of the year. Let the good times roll in a durable T-Shirt that takes kids from school to play in an amazing array of colors. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar.