It is commonly known that the minimum recommended thread engagement to make a strong connection for a component with a tapped hole is approximately 1 times the nominal diameter in steel and 2 times the nominal diameter in aluminum.
Then, what is the typical thread engagement percent?
Secondly, how far do NPT threads engage?
After final tightening using the “Turns Past Finger Tight” method,
|NPT Fitting Assembly|
|NPT Size||Turns Past Finger-Tight*||Thread Engagement Length (Approximate)**|
|1/8 NPT||1.5 to 3||1/4″|
|1/4 NPT||1.5 to 3||3/8″|
|3/8 NPT||1.5 to 3||3/8″|
How many threads should be beyond the nut?
How many threads should protrude through a nut in an optimal joint? The generally accepted answer is 1 to 3 threads. Most externally threaded fastener blanks are manufactured with a header point prior to thread rolling, which leaves the first 1 to 2 threads undersized for ease of assembly.
To determine the ideal minimum drill depth, start with the basic rule: the tap drill depth should be at least one thread or one pitch beyond the chamfer of the tap. In other words, for a 1/4-20 tapped hole requiring a 3/8″ (.
Threads are typically the weakest part of a bolt and most likely to be the cause of failure/fracture when in pure tension. Calculating and understanding the area of the bolt providing strength in tension will help in understanding how the thread engagement length can increase and decrease the strength of a joint.
Thread engagement is the amount of pipe thread nec- essary to make a tight connection between pipe and fit- ting. Refer to T on Figure 1. For the length of thread engagement for the various nominal diameters of pipes, refer to T on Table A.
A generally used practical calculation method for the tread stripping strength is given by the formula Ath=0.5?d0L0. where d0=(d2+d3)/2. Applying this formula results in the effective length of thread engagement of L0=11.5mm.
Another way to measure thread pitch is to place a steel rule down into the axis of a screw and then count the number of thread crests in a given length from that point. The pitch can be calculated by dividing this count by the length.