Johnson Controls wire clamp

[iam4]

Anybody who uses a Johnson Controls A419 for temperature controls...if yours has a plastic "wire clamp" at the bottom to keep your wires snug and from pulling away from the box, could you please let me know exactly what it's called? I've seen metal Romex clamps for metal electric boxes but I'm really looking for the plastic variety. I think the diameter of the hole is around an inch.

Thanks!