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Question:

I have a question about tap end studs for studded adapter flanges. I see two types, some with a body in the middle the same diameter as the threads, and some with a reduced diameter body. Can I use the reduced diameter body type for adapter flanges?

Two methods of manufacturing tap end studs have become fairly standard, thread cutting and thread rolling.

The oldest and probably most common method uses nominal size bar with the threads made by cutting them to desired length on each end. This method leaves a full diameter body on the stud. Persons installing tap end studs with a full diameter body can tighten them firmly in their respective tapped holes, "jamming" them, so they resist inadvertent removal when persons break-out connections in the field. Cut threads have a higher cost to manufacture than other methods of threading.

Tap end studs with bodies smaller in diameter than the nominal thread size have threads produced by a rolling process. Rollers deform the material of a pitch diameter bar, crushing the bar to the thread root depth and raising displaced material to produce the thread crest. Persons installing this type of tap end stud, with a body smaller than the nominal diameter, can easily over-drive the tap end stud into the tapped hole producing variation in the studs extension from the tapped face. Less friction between the "jammed" tap end stud and the tapped hole may allow the stud to back out inconveniently when persons break-out connections in the field. Rolling threads on pitch diameter bar provides the cheapest way we know of to make tap end studs.

Manufacturers may also make tap end studs with rolled threads by taking cut lengths of nominal diameter bar and swaging down the ends to pitch diameter, then rolling the threads on each end. This method of manufacture produces a tap end stud that seems identical to a cut thread stud, in appearance and function. This method of producing threads produces work hardening and stress risers that add a variable that may produce unexpected circumstances. We believe this method of producing tap end studs has resulted in field service failures (Not yet proven).

Currently at WOODCO USA we use and sell only cut thread tap end studs.

For more about Tap End Studs for Adapter Flanges, See Q & A 27.

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