Half Check Collars: That's a type of collar for dogs that have a larger neck than the head, or simply have mastered the ninja-way of escaping from a standard collar with a buckle.
 
Half check collar prevents sudden escape by reducing the circumference of the collar when pulled. When a dog is pulling, the circumference decreases to a fixed point.
 
The adjustment range of the collar does not include the length of the clamp strap:
XS, S - 2.3' (6 cm)
M - 3' (8 cm)
L, XL - 4' (10 cm)