In DesignShop, if you right click on the 3-D icon the window below opens.
Thread width is 3.8 pts. by default which is for normal 40 weight thread.
2.6 pts. would be a starting point for 60 weight thread.
It is important to note that you can only set the thread thickness for all colors in a design, it is a DesignShop global setting, not a per thread color setting.