After testing multiple Golf Tee models online, I came to the conclusion that they all had a major problem - they were designed to be printed upright. This made them very weak, due to the “grain” alignment being paralel to the golf club strike. 

I designed these “FLAT” style Tees to be printed laying down - noticeably increasing their strength. They can still break, depending on the swing, but I have played 9 holes with a single 10mm Tee before losing it in the grass.