2.0x3.0mm: Has a thinner protective buffer (3.0mm) around the fiber. This makes it more flexible and smaller in diameter, ideal for indoor, behind-furniture, or inside enclosure use.

2.0x5.0mm: Has a thicker protective buffer (5.0mm) around the fiber. This makes it stronger, more rigid, and more durable, ideal for outdoor/indoor transitions, longer drops, or areas with more potential for pinch or crush.

2.0mm: This refers to the diameter of the fiber core itself, which includes the bare glass fiber and its primary coating. This part is identical in both cables.

3.0mm or 5.0mm: This is the critical difference. It refers to the diameter of the tight buffer that is immediately extruded over the 2.0mm fiber core. This buffer is the first line of mechanical protection.

In practice, many installers will use the more robust 2.0x5.0mm cable for the entire drop from the pole to the interior ONT to ensure maximum reliability, and then use a shorter, more flexible 2.0x3.0mm patch cord to connect the ONT to the customer's router.