If you only buy one size of Easy Arranger, make it this one!  Our 6 inch Easy Arranger is designed to fit a lot of different vases. 
Remember the Easy Arranger is designed to bend over the top of the vase so you always want it a little bigger than the vase opening.  This arranger is great on vases with a diameter of 5-5.75 inches such as:
Dozen rose vases from the florist
Hurricane style vases
Cylinder vases
Small bowls