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What types of special heads are available for the Fowler/Bowers bore gages?

What is bore measurement?

Simply put, bore measurement is the measurement of holes. Bore measurement can be accomplished using a number of tools including micrometers, calipers, and gauges. There are a number of reasons you might need to take any number of measurements of a bore. Today, we would like not to talk about bore measurement generally, but instead to focus on some of the specialized metrology instruments designed for unique bore measurement applications. We hope that the Bowers and Fowler tool heads we outline today help ease some of the challenges faced with more complex bore measurements.

Specialized bore measurement and head requirements

When it comes to bore measurement, Fowler and Bowers are two of the go-to brands. Bore measurement is commonly done using a bore gauge or an inside caliper. These tools are used to measure the internal dimensions of a hole or bore. Fowler and Bowers know that while the average bore measurement can be done using a standard instrument, often metrologists run into trouble when working across more unique applications. Additionally, sometimes you need a specialized tool for a specialized bore measurement. That is why Bowers and Fowler carry their family of specialized heads. These caliper and gauge heads are specifically built to be used for non-standard applications and to help you solve measurement problems encountered in day-to-day circumstances.

What types of non-standard measurements are done using Fowler and Bower specialized bore heads?

Measuring dovetail slots and turbine blade grooves



Depending on your profession, you might need to measure dovetail slot width, dovetail slot position, or both. Some industries that measure dovetail slots include power generation, nuclear engineering, turbine manufacturing, and aerospace. As is known, the shape of a dovetail slot is quite different than the average bore. In this instance, measurements are commonly taken from the shoulder of the slot and applied to the entirely of the bore. Fowler and Bowers took on this challenge and created an XT head with a 2-point head made with tungsten carbide ball contact points. Therefore, this tool is capable of providing the actual size and position within a dovetail slot, has a low rate of wear, and can be used for the long term. Additionally, with digital readout and data transmission, this specialized head is built for part traceability and quick data transmission. The possible bore measurements include: single side measurement for set-up and symmetry, double side measurement for overall width, measurement of dovetail seat face width, and measurement of bottom lobe width.

Measuring surface and subsea valve cavity-seat pockets

Industries such as oil and gas, hydraulics, and pipework sometimes need to measure the internal cavity in valve bodies. Taking the measurement of the internal cavity in valve bodies comes with a particular set of features that are required. These features include: the internal spot face to diameter measurement, internal spot face distance between flats, and internal diameters inside seat pocket. In response to this particular need, Bowers and Fowler solved the problem using a one-piece right angle adapter that allows for entry down into a bore that is perpendicular. Thus, measurements can be taken at a 90-degree angle compared to the bore entry. The measurement head is then positioned using an optimized anvil form in conjunction with guide pieces. This increases bore measurement accuracy, makes the tool easier to use, and allows for faster inspection.

What specialized Fowler and Bowers XT heads are available?

Fowler and Bowers XT thread heads


Bore measurement may require adaptation when completing simultaneous thread measurement. The Fowler and Bowers XT line includes a head for screw threads with additional 2-point and 3-point models. These heads can be used to measure functional diameter as well as pitch diameter and major diameter. Diameters can range between the M4 – 300mm and No. 8 UN – 12” diameter. Additionally, there is a ball screw thread model as well as an external thread model.


Fowler and Bowers XT groove heads

When measuring bores that have groves along the sides, a standard bore measurement tool will just not be enough. That is why the Bowers and Flower XT line offers specialized heads built for grooves, brake caliper measurement, and ball race measurement. These are interchangeable heads, that come with a special form, radius, and ball contacts. If you are working with measurements that require quick location, each model is available with an attachable depth stop. These tools are even built to work with annular grooves.

Fowler and Bowers XT internal spline heads

Splines are a type of slat that are shaped like a rectangular key that fits into grooves in the hub and shaft of a wheel. As you might expect, bore measurements involving splines are pretty advanced. The Fowler and Bowers internal spline heads come in 2-point and 3-point designs, are built with anvils made entirely from steel, and offer pitch, major, and minor diameter heads. The specialized devices can be used with any diameter between 8 and 300mm.

Fowler and Bowers XT external spline heads

Splines do not just require internal measurements. That is why Bowers and Fowler did not stop there and also introduced the external spline heads in the XT line. These come with identical features and capabilities to the internal spline heads, but also have frames that are fitted with 1 x ball and 1 x pin.

Fowler and Bowers XT spherical heads

Spherical heads may sound straightforward, but in the atypical bore measurement world these specialized heads come in very handy. In the Fowler and Bowers XT heads line there are 2-point and 3-point spherical heads. The 2-point spherical head can be used for taking measurements of the ovality in a bore or when working with bores that have irregularities. The 3-point spherical head offers excellent bore measurement repeatability, even under circumstances when the head must be out of line with the center of the bore. These are available for diameters of 6 to 300mm. Additionally, a spherical radius is available for both models.

Fowler and Bowers XT deep hole pneumatic heads

The Bowers and Fowler XT deep hope pneumatic heads come equipped with the following features: spherical anvils made of tungsten carbide, 2-point or 3-point heads, quick set-up time, ease of use, protection from temperature fluctuation, various types of readouts, and a robust design. These specialty heads have an accuracy of +/- 0.005mm that may be dependent on the condition of the bore itself. Additionally, they are capable of measuring diameters from 50 to 310mm that are up to 15m deep. The Bowers and Fowler XT deep hope pneumatic heads are powered by a 3-bar compressed air supply that help to operate the pneumatic actuator. All data collected when conducting measurements is done so through the capacitive probe fitted behind the head maintaining constant contact. These tools have the highest quality transducer-type accuracy at up to 15 meters of depth. By pressing down on a footswitch connected to the airline, you have taken your measurement. Data is quickly transmitted through a cable to the operator end of the tool for a digital readout.

Fowler and Bowers XT miscellaneous heads

Fowler and Bowers did not want to miss any type of non-standard bore measurement situation that required a specialized tool. Within the XT line of specialty heads there are a number of miscellaneous heads that may come in handy. The irregular spacing heads come with between a 16 to 300mm diameter in order to measure between oddly spaced lobes. The gun barrel head offers simple measurement of a smooth bore and rifled bore gun barrels, with both major and minor diameters that measure at a great depth. The blind bore head comes standard between 2 and 6mm as well as 12.5 and 300mm, but can be made between 6 and 12.5mm upon special request. The slot width (small) head measures small slots with widths between 2 and 6mm, while the slot width (large) head measures large slots with widths between 6 and 100mm. The right angled adapter head helps metrologists when struggling with bores that require measurements at right angles.


Bowers and Fowler work hard to keep up with customer needs. In response to a growing application of bore measurement in non-standard ways, these companies created a line of specialized XT bore heads. These unique tools help metrologists complete thread, groove, internal spline, external spline, spherical, deep hole pneumatic, and other miscellaneous bore measurements. Browse the online catalog or get in touch with a specialist at Higher Precision today to learn more about how these specialized heads can change the way you measure bores.


Why is it necessary to have a line of specialty heads for bore measurement?

Bore measurement is one of the most common measurement tasks required of metrologists. Whether working in machining, aerospace, engineering, or any other number of industries, holes or bores are involved. What is less commonly known about bore measurement are all of the non-standard situations in which bores need measuring. Perhaps you are working with a bore that is angled partway through, or one in the shape of a dovetail. There are a number of unique bore circumstances that get overlooked in the world of specialized tools. Well, Fowler and Bowers wanted to amend this situation and so they created their line of XT specialty heads to help you measure bores of all shapes and sizes. The caliper and gauge heads in the XT specialty collection are designed for a number of non-standard bore measurements in order to help you solve any problems you may be encountering on the job.

What specific heads are available in the Bowers and Fowler XT heads line?

The heads available in the Bowers and Fowler XT heads line cover all of your bore measurement needs. Each specific head comes with a particular purpose to which it can be applied. The types of heads available include: thread, groove, internal spline, external spline, spherical, deep hole pneumatic, irregular spacing, right angled adaptor, gun barrel head, blind bore, slot width (large), and slot width (small). Additionally, Fowler and Bowers took the time to answer the challenge of measuring dovetail slots and turbine grooves. If you work with the internal measurement of surface or subsea valve cavity-seat pockets, then look no further because they covered that too.

Why did Bowers and Fowler design, test, and produce the specialty XT line of heads?

Bowers and Fowler are top in their field of precision measurement tooling. They are up-to-date with the latest technology and trends, and work to maintain the highest quality in both design as well as production. Above and beyond these qualities, Fowler and Bowers have the customer in mind. They aim to hear from the customer perspective about what it is really like to be taking measurements across all kinds of situations. So it was in response to a real need that Bowers and Fowler decided to design, test, and produce the specialty XT line of bore measurement heads. You asked and they answered. The field of metrology is an ever-changing industry and the tools available impact numerous people every day at home and on the job. As sellers and producers it is our main aim to supply our customers with what is in demand. That is the motivation behind this amazing line of specialty bore measurement heads.


Bore Measurement

Bore measurement is the process of getting the internal dimensions of a bore. The dimensions typically collected include depth, width, diameter, and sometimes angle. Bore measurement can be completed using a gauge, a caliper, or a micrometer. While most bores are straightforward to measure, there are some non-standard bores that require specialty tool design, such as the Bowers and Fowler XT specialty heads line.

Dovetail Slot

A dovetail slot is a particular type of bore that is designed to be matched with a dovetail anchor. This uniquely shaped hole has the base of a triangle that then opens up at the top with two extensions outward from the walls of the base. Given the complex design, the dovetail slot is particularly effective at anchoring one part to another while allowing for sliding movement along the length of the slot.

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