Alpha 1 leather martingale collar gives you the control of a choke collar without over choking.  The leather is gentle to the neck.  Excellent collar for show and leash training puppies.  Size is diameter of the open measurement.  Order size comparable to the choke chain size for your dog or measure your dog's neck and add 2-3 inches.  Make sure size is large enough to slip over your dog's head.  May not be suitable for some breeds with a large head (see our adjustable bullhide martingales).