How do you mean? Ive not had to cut one yet. CU's normally come with a 32mm knockout, Can use a stepdrill if you need to make it bigger for whatever reason.But you wouldn't get 2x 16mm tails in a 20mm stuffer would you? And if the tails are 25mm?
The only issue with the bigger gland is cutting the damn hole. But the bolt up plate cutters make quick work of it.