Disclaimer: this idea came from this.
Enjoy clipping things to tubes of all sorts, in the example I used a pretty standard bike tube and clipped a small flower pot to it.
Step 1: Step 1: Find the Diameter of Your Tube
Get the diameter of your tube, any tube, and model it. Remove 75% of the ring to allow for the opening of the model to fit onto the tube. Depending on model thickness, layers, plastic type used, etc. you may need to adjust the 75% rule. The model was made after several tests for "snap" on my particular handle bars.
Take this new line, model closure, and extrude to create the clip.
Step 2: Step 2: Join the Clip and a 3D Model
Take any shape you would like to attach to the tube and join it to the clip. This can be done many times with many different models, so feel free to experiment at this point after a test print that the clip fits the tube.