In the field an "about right" dimension means either a leaking joint or a stripped nut. Three dimensions must be given together when ordering studs: diameter, thread and length.
Diameter and thread
Stud diameter follows the bolt hole diameter of the flange; a stud about 3 mm smaller than the hole is standard practice. On the thread side there are two systems:
- UNC (coarse): Common at 1 inch and below in the ASME world
- 8 UN (constant pitch): Standard from 1 1/8 inch upwards
- Metric (ISO): Used with EN flanges
The thread system must match the nut; a metric nut does not fit a UNC stud.
Length calculation
Stud length is the sum of the first flange thickness, gasket thickness, second flange thickness, two nut heights and thread allowance at both ends. Standard practice leaves about two thread pitches proud at each end.
What changes the calculation:
| Case | Effect |
|---|---|
| Blind flange | Thicker than other types; length increases |
| Isolation gasket set | Sleeve and washer thickness is added |
| Spectacle blind | Adds the plate thickness |
| RTJ face | Groove depth enters the calculation |
| Washers | Each washer adds length |
A stud that is too short leaves the nut without full thread engagement and the joint loses capacity. Overly long studs cause confusion during assembly.
Material grade
A193 B7 studs with A194 2H nuts are standard on process lines. B16 takes over at high temperature, L7 at low temperature and B8/B8M in stainless service. NACE MR0175 hardness limits apply in sour service.
When ordering
State diameter, thread system, length, material grade, coating and quantity together. Ordering studs on the same list as flanges and gaskets prevents length errors.
See our studs and nuts page and send your list through the enquiry form. For tightening see flange bolt torque.
FAQ
How is stud length calculated?
The sum of two flange thicknesses, gasket thickness, two nut heights and the thread allowance left at each end.
What is the difference between UNC and 8 UN?
UNC is a coarse thread used at 1 inch and below; 8 UN has a constant pitch and is standard above 1 1/8 inch.
Why is stud length different on a blind flange?
A blind flange is thicker, so total thickness and the required length increase.
Send us your material list; we reply with price and lead time the same day.
Request a quote