McDonald’s can rightly claim that they are America’s favorite French fries and they use a shoestring fry. They have more units than any other burger chain by far and fries were an important part of the limited menu they had for years. As you may recall, at one time you could “Supersize Your Fries” for about 39 cents and even before that they offered a small, medium, large and at one point the extra large portion sizes. McDonald’s is said to own some 17% of the limited service restaurants in the USA and their total food and beverage volume is nearly as much as the next four combined.

Your second question seems related to fresh fries and the preference shifts to a thicker fry, usually the 3/8ths inch cut. There are two reasons…. Cutting russets into smaller strips takes a lot of muscle and the larger cut fresh fry usually has the skin left on, signifying it was made on premise.

The question about the end of the season… this is typically July and August for Russet Burbank’s. In Idaho they start up again mid-September to mid-October. Russet Norkotahs are the first fresh variety harvested, typically in August to September. At the end of the season the potatoes may fry up faster, having lost some of the moisture. They can also accumulate sugar if stored too cold.

Start out by blanching at 325 degrees, finish fry at 350 degrees F. Blanching at a lower temp will help the fries from turning too dark, but takes a little longer.

 Several articles about this at the link “All Things French Fried Potatoes”: