The size of the spinner is the measurement at the rear lip of the dome. If the spinner is made with the length of the dome left intact, the size is as shown in the descriptions.
The "10" spinner is actually 10.375". If it is installed without being shortened, it is 10.375". If it is installed with an IVO Patriot, which is only 1.375" thick, the dome is cut shorter and will be 10".
All our spinners are sent out balanced to a tolerance of about 1 gram (28grams = 1 ounce). For example, if you remove one of the 8-32 x 3/4" dome mounting bolts from a balanced spinner and put it back on the balancing rig, it shows as being "sharply out of balance".