These straps are made of 2" webbing and close with a 4" long strip of overlapping industrial grade velcro (straps under 24" will have a 3" long strip). They are extremely secure. The reason that these straps are so great is because they use the rectangular ring at the center to provide a fulcrum for the webbing. This allows for the webbing to be pulled very tight, because the fulcrum enables doubling the force that is put on the strap.
How to size: The straps are capable of sizing down to approximately half their overall length. For example, a 72" strap will be able to secure a diameter between 68" and 40". A 48" strap would be from 44" to 28".
The polypro webbing itself is two inches wide and has a breaking point of 1000 pounds, so it is extremely secure yet comfortable to wear.