Ultimate Side Reins are custom sized and made of high quality, light weight 1" wide polypropylene. Each set  comes with 16 total D rings (8 per rein), a bolt snap on one end and a quick release snap on the other. Bit snaps for easy attachment are included. All of the D rings and snaps are nickel plated and treated with a protective, rust-proof coating. Please remember that this is a custom made product and shipping times will vary. Elastic Inserts and are also available. Sizes are as follows - Medium - 83.5" for horses  14 - 15.1 Regular - 87.5" for horses  15.1 - 16.3 XLong - 91.5" for horses  16.3 or taller. If you are uncertain of sizing due to neck length or body thickness, please see image and tips below. This method is not an exact science but should help. Measuring for side reins: 1.Stand horse squarely with head relaxed. 2. Tie one end of twine to bit ring and stretch to girth area or to first billet. 3. Cut the twine at the edge of the billet and below the knot on bit. 4. Measure the length of twine. 5. Double the measurement and compare to lengths on drop down menu.