Tommy Hole Nuts

When a joint is tightened with a hydraulic bolt tensioner, the tool pulls on the end of the stud and stretches it. While the stud is held under load, the nut is turned down against the joint through a window in the tool, usually with a tommy bar (Hi-Force tensioner manual). The pressure is then released and the nut holds the stretch in the stud (Assembly Magazine).

Some tensioners turn the nut with a drilled socket that fits over a plain hex nut. Others turn the nut itself, and for those tools the hex nuts must have tommy bar holes (Boltight subsea tensioner manual). Drilled nuts are also used where there is no room to swing a wrench.

We drill tommy holes to suit your tool and your joint. Tell us:

• Number of holes and how they are spaced around the nut.
• Hole diameter and depth, or the tommy bar you use.
• Hole position on the flats and its height on the nut.
• The tensioning tool, if you are matching an existing tool.

If you send a drawing, we make the nuts to it.

We make tommy hole nuts in the nut grades we already make, matched to the stud grade:

• ASTM A194 2H for A193 B7 studs
• ASTM A194 2HM for A193 B7M studs in sour service
• ASTM A194 Grade 7 for A193 B16 and low-temperature studs
• Nickel alloy and stainless grades, such as Inconel heavy hex nuts

Compare grades in our Fastener Materials Matrix.

Tensioned studs are usually longer than torqued studs because the tool needs thread above the nut to grip. Our stud bolt length calculator and bolt tensioning pressure calculator can help you plan. We make the studs and nuts together so the order arrives as a set.

What is a tommy hole nut?

A tommy hole nut is a heavy hex nut with radial holes drilled into its flats. A steel rod, called a tommy bar, fits into the holes so the nut can be turned where a wrench or socket will not fit.

Why do tensioned joints use tommy hole nuts?

A hydraulic bolt tensioner stretches the stud, and the nut is then turned down against the joint through a window in the tool, usually with a tommy bar. Tensioner makers note that the hex nuts used with some tools must have tommy bar holes for this step.

How many holes do you drill, and where?

We drill the number, size and position of holes shown on your drawing or called out for your tensioning tool. If you do not have a drawing, tell us the tool and the nut size and we will confirm the details with you before we make the parts.

Which grades can you make tommy hole nuts in?

We make tommy hole nuts in the same nut grades we make our heavy hex nuts in, including ASTM A194 2H, 2HM and Grade 7. Tell us the grade on your purchase order and we will confirm it.