Which Indicating Bore Gage Should You Get?

Which Indicating Bore Gage Should You Get?

If one selects the wrong type of bore gage, it
could deliver inaccurate data, low throughput and end up as an unnecessary
expense. If you are looking to get indicating bore gages, here’s what you need
to know:

Understanding the Basics of Indicating Bore

The two basic types of indicating bore
are fixed-size gages with plug-style housing and adjustable-capacity
gages with interchangeable extensions or contacts. In most cases, indicating
plug gages offer higher repeatability and can measure closer tolerances than
their adjustable counterparts. Now that you have a better understanding of
indicating bore gages, below are several factors to consider before choosing
the ideal bore gage for your precision measurement needs.


If you need to measure large inner diameters (ID), adjustable bore gages are currently recognized as the economical option. Stock adjustable gages and masters are typically available in capacities of up to 24 inches. Most plug-type gages, on the other hand, are over 4.5 inches and are considered “specials.” This means that they cost slightly more than adjustable gages.


Today, many modern shops still utilize adjustable
bore gages. In addition to low production runs, adjustable bore gages come in
handy when technicians need to measure with medium to broad tolerances. Additionally,
the application might have many different bore sizes to measure as well. The
range of these gages is typically up to three times greater than that of plug
gages, i.e. 0.010 inch vs. ≤ 0.006 inch. That’s why they are practical to use
with broader tolerances.

Because adjustable gages can measure a range
of hole sizes, some shops only require just three units, with capacities of:

  • 0.500 to 1.00 inch
  • 1 to 2 inches
  • 2 to 8 inches

Indicating plug gages, on the other hand, require
separate size plugs to measure each hole size.


One of the biggest advantages of fixed-size
plug gages is that they can eliminate “rocking” to center the gage in
the bore. Self-centering plug gages virtually eliminate operators’ influences
and require minimal training. Rocking adjustable gages is considered a refined
skill that needs to be performed conscientiously. Inadequately trained
operators who are rushed or tired are likely to produce inaccurate results.

Adjustable gages, on the other hand, are more
subject to intentional operator influences than the aforementioned gage. This
is called “close-enough syndrome.” If you want to eliminate
“rocking” and speed up the measurement process, choose plug gages.
They perform well in production runs where tolerances are tight, and volumes
are high. Additionally, they have larger bearing surfaces, are more resistant
to wear, and offer greater repeatability. It is recommended that one uses plug
gages with electronic data collection systems.

Willrich Precision is the leading supplier of precision instruments including bore gages. We have over four decades of experience supplying high-quality precision measurement instruments to a variety of industries. You can count on our professional staff to offer advice and suggestions when you are buying equipment from us. This way, you get the correct products for your applications and save money. Willrich Precision is also a family-owned business and we put our customers at the center of everything we do.

by George Chitos