The propellers have different names, for example, 10 x 4.5, 7 x 3,7, 8 x 4. How they should read?
These figures mean parameters, expressed in inches. The first of them refers to the diameter of the screw, and the second is jump, which will win screw at full rotation:
The jump can be considered as the distance that will overcome the flying machine with one complete turn of the screw (in ideal conditions with zero mass). This parameter means the same thing in the case of the bolt thread.