Here's a project for costumes, cosplay, cats, dogs, and lovers of tailed creatures.

 The bulk of the project is 3D printed... only a few additional items are needed.

• Silicone tubing ~12 mm (outer diameter)
• Beadalon stringing wire .61mm
• Standard Metal Gear Servo
• 30mm screws (almost any kind wil do - you only need two)
• 10mm screws
• 8mm screws
• Spring from a ballpoint pen

And, some basic tools.

• Hot glue gun
• Silicone adhesive
• M4 tap (optional)
• Wire cutters
• Screwdriver

Silicone tubing has an outer diameter of ~12mm and an inner diameter of ~9mm.

Thicker stringing wire is better - your tail will last longer and will be more durable.