They are made with thick nylon with ribbon sewn on, and adjustable. Any size can be done,
Metal Buckles are very strong, can hold up to 200lbs or more weight. Never had one snap
 
ONLY AVAILABLE IN 1 INCH WIDTH
 
Sizes are: 
Medium 12 - 17 inches adjustable
Large 15 - 23 inches adjustable
XLarge 22 - 39 inches adjustable
 
Please visit the PATTERN PAGE for pattern options: https://www.craftdoghandmadepetsupplies.com/patterns