How do courser and finer threads relate to TPI? The variation in the coarseness and fineness of the thread of a screw impact the threads per inch. These differences also change the weaknesses and strengths of the screw, making it more or less ideal for a particular use. A greater number of threads can fit into an inch of length when the screw is made up of finer threads, meaning it has a higher TPI. A fewer number of threads can fit into an inch of length when the screw is made up of courser threads, meaning it has a lower TPI. Some of the strengths of a screw with finer threads, or a higher TPI, include being stronger in higher tension due to larger stress areas, as well as higher shear strengths and the ability for very close adjustments. Some of the strengths of a screw with courser threads, or a lower TPI, include a lesser likelihood of cross threading, a greater amount of resistance to fatigue, and allowance of thicker coatings and platings.