Add a martingale chain to any collar in the shop. Choose your finish.  Martingale chains are perfect for pups that pull as it tightens up so they cannot slip out. 
 
You will order the same size as you would for the O ring style as this is made to slip over the head. Measure your pup with a soft measuring tape around the biggest part of the head and the neck area. Choose the bigger of the two measurements.