No pull harness fitting

When the harness is properly adjusted, the front strap must release the point of the dog's shoulder to avoid impeding movement (2) and clear the dog's trachea (1).

It's important to tighten the front strap sufficiently so that it doesn't slip down the dog's neck.

The ribcage strap should be tight enough to ensure the harness's stability on the dog.

For the front adjustable straps, you should be able to pass a hand between the dog's body and the strap to make sure it's not too tight. 

Too large

If the harness is too large, the front strap will be too low and will pass over the dog's shoulder tips (3).