In my case the spacers are temporary. I don't intend on keeping them as I will not take any chances of losing a wheel at highway speeds. You'll have to decide for yourself if they are safe or not. Here is are a couple of links I came across when researching the topic. "Make sure you have a minimum thread engagement of the diameter of the vehicle stud (as recommended by SAE). An example is, if the stud size of your vehicle is ½" then you will need a minimum of ½" of threads into the lug nut."
http://www.performanceplustire.com/t...rs-and-Spacers
http://www.performanceplustire.com/t...about-lug-nuts