How is the size stub determined based on bolt hole size?

The size of a stub, particularly when working with flanges or fittings that require bolting, is often determined by the bolt hole size because it ensures proper alignment and fit between mating components. When the bolt hole size is known, subtracting an eighth of an inch helps accommodate the thickness of the material surrounding the bolt hole and allows for a good seal without being too tight.

This practice takes into account factors like material expansion, flex, and potential warping, ensuring that the stub remains functional while maintaining connection integrity with the bolts and associated hardware. Proper sizing contributes to the reliability of the whole piping system, as mismatches can lead to leaks or mechanical failures.

In general, the other options—adding a quarter inch, halving the size, or doubling the size—do not align with standard industry practices for determining stub sizes based on bolt hole dimensions. These would risk compromising fit and function, which are critical in pipefitting.