Wherever there is milkweed there will be Monarch butterflies. The monarch is widely distributed across North America, from Central America northwards to southern Canada, and from the Atlantic to the Pacific coasts.
The pitch diameter (often called the effective diameter) of a parallel thread is the diameter of the imaginary co-axial cylinder which intersects the surface of the thread in such a manner that the intercept on a generator of the cylinder, between the points where it meets the opposite flanks of a thread groove, is equal to half the nominal pitch of the thread.
For diametral pitch, the # means how many teeth will fit on a pitch circle of 1 diameter. For metric module, it is the arc distance x Pi along the pitch circle from one tooth to the next. So, a 16DP gear with 32 teeth has a pitch circle of exactly 2 diameter. If you straightened out the gear, the teeth would be 1/16 x Pi apart. A 2mm metric module gear with 32 teeth has a pitch circle of exactly 64mm diameter. If you straightened this gear out, the teeth would be 2mm x Pi apart. There are a gazillion other parameters and formulas for the rest of the gear form.