<Li> The roots and crests of mating male and female threads need clearance to ensure that the sloped sides of the V meet properly despite (a) error in pitch diameter and (b) dirt and nick - induced burrs . </Li> <Li> The point of the threadform adds little strength to the thread . </Li> <P> In ball screws, the male - female pairs have bearing balls in between . Roller screws use conventional thread forms and threaded rollers instead of balls . </P> <P> The included angle characteristic of the cross-sectional shape is often called the thread angle . For most V - threads, this is standardized as 60 degrees, but any angle can be used . The cross section to measure this angle lies on a plane which includes the axis of the cylinder or cone on which the thread is produced . </P>

What is the difference between nc and unc threads