Interesting fact: If you’ve ever designed a part with a tapped hole, you may have wondered, “How many threads do I need to make a strong connection?” The answer is that it varies, but six at most.  Because bolts stretch slightly when load is applied, the loading on each thread is different. When you apply a tensile load on a threaded fastener, the first thread at the point of connection sees the highest percentage of the load. The load on each thread decreases from there, as seen in the table below. Additional threads beyond the sixth will not further distribute the load and will not make the connection any stronger.