Using a sharp utility knife, score the plastic casing all around. Locate the cut at about half of the casing’s length length.

Important: Take extreme care with your fingers due to the small size of the casing, the smooth and slippery surface of the casing, and how close your fingers will be to the blade when doing this.

Make the score lines as perpendicular to the casing as possible, and make them meet at a point after going around the casing. This will make the next step a lot easier. Marking out the score line with a permanent pen before scoring would help.