The revolutionary BIRTEE PRO golf tees are designed to be fast and easy to use for golfers of all calibres and ages. People love their consistency. They are also very durable and recyclable and are Made in Canada. They provides every golfer with a constant height for any size club (Drivers, Woods, Hybrids & Irons) for every tee shot. The 8 sizes conform with USGA & RCGA Rules of Golf and the U.S. Patent was also granted on May 31, 2011. The BIRTEE PRO works on normal golf surfaces, as well as on any hard surface such as gym floors, indoor GOLF SIMULATORS and frozen ground making them perfect for winter use. It was designed to be reusable, durable, recyclable and more convenient than conventional tees. It eliminates the need for pushing tees into the ground, but most importantly it eliminates the guess work for achieving a constant tee height. The 8 constant heights will give every golfer more confidence and consistency. IMPORTANT: If you ordered these for a Golf Simulator then please read to get the best results.If you have a: Full Swing, About Golf, SkyTrak or Optishot then the White and Lighter Colors may cause misreads. It is better to choose a darker color like: Dark Blue, Black, Green or Purple.For Uneekor, the light colors, but also the Red and Purple may cause misreads therefore the Black and Dark Blue are the best colors.If you have a TruGolf Simulator or Trackman then the color doesn’t matter therefore the White or Yellow will work fine. See other listings for other sizes. Sizing Guide: #1 - 1/4" - Use with Irons/Wedges #2 - 1/2" - Use with Irons/Hybrids #3 - 3/4" - Use with Hybrids/Junior Driver #4 - 1" - Use with Fairway Woods / Junior Driver #5 - 1 1/4" - Use with Fairway Woods / Driver #6 - 1 1/2" - Use with Driver #7 - 1 3/4" - Use with Driver #8 - 2" - Use with Driver