1/4-20. The thread size is 1/4-20 - this means that the nominal diameter is 1/4î and that there are 20 threads per inch. When there are 20 threads per inch, the distance between each thread is the reciprocal of the TPI (1/20 = 0.05î).
Keeping this in view, what does UNC mean for a bolt?
What is the difference between UNF and UNC?
Threading – National Coarse (UNC) vs. National Fine (UNF) As illustrated in the chart above, there can be a significant difference in the number of threads per inch between UNC and UNF threading. UNC is the most common general fastener thread; the fit is deeper and is more versatile in its application.
Is BSW the same as UNC?
Be aware that although they look similar, they should not be used as full replacements or be mixed with each other! UNF and BSF have completly different thread per inch value. So they don't fit. UNC and BSW have the same thread per inch value, accept for the 1/2" size.