Dial bore gages are used as comparators. You will be comparing the bore of your work against the bore of a master, such as a ring gage or a preset micrometer. If your work piece has to be .375" for example, place your bore gage head into a .375" ring gage and set the dial to zero. Then place the bore gage head into your work piece and you will be able to see how close to zero your bore is. The graduations on the dial, be they .0001" or .0005" (or metric) will indicate the difference between your work piece and the ring gage.

Bore gages typically have 2 point measurement. The fixed—but interchangeable—range contact is opposite the movable measuring plunger. This arrangement allows you to check for irregularities in the bore. You'll easily see if you're out of round, or if you've created a taper.

There exists a split head style of bore gages, Diatest and Mitutoyo being notable. While these are also used as comparators, they can not be used to check the geometric shape of the bore because they don't use two point contact. If that's something you need to check, then you will have to eschew this style. They have the advantage of fewer moving parts and can be less prone to mishandling.

Dial or digital bore gages can not measure to the very bottom of a blind hole because of their design. However, Mitutoyo makes a bore gage which can get within 2.5 mm of the bottom. The other styles are best used on through holes.

Since direct measurements are never taken with a bore gage, there is little point in having the gage calibrated. What is important is that the indicator hand moves freely and the gage doesn't stick; that there is no excessive play in the movable anvil at the measuring head; and that the fixed or interchangeable anvils (there may be one or more) are not worn flat. If any of these conditions exist, then the gage needs servicing. The dial indicator which is attached to the measuring head must, of course, be accurate and this indicator can be calibrated just like any other dial indicator. (See this web site for information on dial indicators.) Please note: if you need to take direct measurements of the bore then you'll want to use an internal micrometer or a bore micrometer such as an Intrimik or ingage.

Bore gages are available from many manufacturers with a great range of prices which are a reflection of the tool's durability and workmanship. Gages with carbide plungers and points will of necessity cost more but last longer. On the other hand, steel plungers and points are cheaper to buy and replace. As with other gages, if the tool will only be rarely used there is not much sense in investing in high-end equipment. All bore gages are accurate comparators when new, whereas the better brands are likely to last longer. (We are still repairing Compac dial bore gages that were made in the 1950's.)

An important consideration when buying a dial bore gage: all bore gages use a series of extensions and contacts; these parts eventually wear down or get lost and you will need replacements. Be sure to buy a bore gage that has replacement contacts and extensions readily available otherwise you will be left holding a useless piece of equipment.

The measuring head and the indicator portion can usually be purchased separately if one or the other becomes damaged. Replaceable anvils and other repair parts are generally available except for the inexpensive models such as Teclock and other generic Asian imports.

Alina

Alina dial bore gauges were manufactured in Switzerland and discontinued in the late 1960's. They were American versions of the early Compac dial bore gage. It's a testimony to the skill of this manufacturer that these gages are still in circulation. Parts for the measuring head are identical to current Compac models (see below). The dial indicator has been replaced with a newer version but it is no longer sold separately.

Asimeto

Aimeto are a new branded bore gage of Chinese origin coming from a Hong Kong distributor. They appear to be no different from other Chinese gages and bear a close resemblance to the Mitutoyo bore gages. Parts may be difficult to obtain.

Boice

Boice formerly manufactured by Federal Gage. These are discontinued.

Bowers

Bowers made in England and distributed in the US by Fred Fowler. Originally designed for the British automobile manufacturers. They have 2 point measurement and depth extensions are available. We have no experience with these and can't pass judgment.

Compac

Compac dial bore gauge manufactured in Switzerland since 1943. Formerly sold with the Alina, Interapid and SPI name on the dial. They have long been the very finest bore gages available. The design and constructions of these bore gages is unlike any other on the market. Metric models are permanently discontinued. Inch models are now only available as special orders which can take up to 20 weeks. They are only made on demand.

Denly

The Denly Comparator was the most accurate dial bore gage of its time... in the 1950's. It was made in Switzerland and subsequently replaced by the even better Compac dial bore gage. Originally sold in the US by Alina Corporation, this set is an antique and parts are long obsolete. If you have one in good condition hold on to it as a mechanical wonder of its day.

Dorsey

Dorsey Standard Style dial bore gage made in USA. Dorsey offers an impressive variety of bore gage styles. Among them are the "Standard Gage" style which is a look-alike of the old made-in-Poughkeepsie bore gages except that they now have a Dorsey dial indicator (which we can only see as an improvement). Parts for the measuring head are interchangeable with the Poughkeepsie and the Swiss models. Deliveries are usually from stock and parts and repair service are readily available when needed. This is the only alternative to the discontinued Standard Bore gage made in Switzerland.

Hemco

Hemco of Holland, Michigan, bore gages made in England. No information available.

Interapid

Interapid dial bore gauge was manufactured in Switzerland by Compac and previously sold by Borel & Dunner. These are no longer being sold under the Interapid name. They are identical to the Compac dial bore gage (see above).

Kent Moore

Kent Moore dial bore gages were manufactured by Standard Gage in Poughkeepsie. Kent Moore tools are usually associated with the automotive industry. See Standard Gage, below.

Mahr

While Mahr puts their focus on highly accurate air gaging systems, they also offer well-built (German) mechanical and digital bore gages, some with .00005" indicator resolution. Measuring ranges from .5" to 8" are available with just 3 different gages. Pricing is reasonable for the quality.

• Information: information@mahr.com or www.mahr.com website

Mitutoyo

Mitutoyo dial bore gages Series 511, manufactured in Japan are an affordable option. These are the best choice for low cost bore measurement because replacement parts and repair service are available. Mitutoyo dial indicators are included with the bore gage. Depth extensions up to 39" are available. Dial bore gage Series 545 is patterned after the Standard Gage dial bore gages but Mitutoyo offers fewer models. Never ones to rest on their laurels most older design Mitutoyo models were replaced by new ones that—on some models—incorporate a small micrometer head making it very easy to set a specific diameter. A separate series is dedicated to the measurement of blind holes

Peacock

Peacock dial bore gages are manufactured in Japan. Apparently the metric models are popular in the auto industry. They're an "economy model" and should probably be treated as throw-aways. Available in ranges from .25" up to 10". A series of anvils and washers are used to get the different bore diameters. For what it's worth, you can get the dial in white or black.

Schwenk

Schwenk dial bore gauge. Made in Germany by Oskar Schwenk using Kafer dial indicators. A light, well made gage available in standard and right-angle versions is sold under the brand name Subito. Any dial indicator with 8 mm or 3/8" diameter stem can be used with this bore gage. They are much less expensive than other European bore gages. These are similar to the ones sold under the name Etalon in the 1950's. Etalon dropped the line when the better designed Compac bore gages were introduced. Tesa's Veribor is suspiciously similar.

SPI

SPI is a vanity dial. SPI had put its name on the Swiss made Compac dial bore gage (see above). Other than the dial, all parts are identical. SPI has stopped carrying these. If you need new gages or spare parts, simply order the original Compac version. Beware of economy bore gages made in Asia, also sold with the SPI vanity dial. The cheap price should give them away. If you want the real thing, make sure it's made in Switzerland. Parts and service for the Asian bore gages are not available.

Standard Gage

Standard Gage no longer makes dial bore gages. For a few years they were made in Switzerland by TESA but this proved unprofitable and the line was dropped. Older models were made entirely in Poughkeepsie, New York. Dorsey Metrology makes a look-alike which they call "Standard-Style Bore Gage." It is worth considering since it is a nearly identical replacement. Parts for the old style and the new Dorsey style are interchangeable. Parts for the small No.0 and No.1 bore gages are no longer available.

Subito

Made in Germany by Oskar Schwenk. A light, well made gage available in standard and right-angle versions is sold without a dial indicator. Any brand dial indicator with 8 mm or 3/8" diameter stem can be used with this bore gage. This can be a real money saver since you can use an indicator which you already have.

Sunnen

Sunnen dial bore gage. These American made models, designed as an accessory for Sunnen honing and bore-sizing machines, have fully exposed measuring heads making them easy to slosh around in cleaning fluid when needed. The current dial indicator is a modified Mitutoyo indicator. Early model Sunnen bore gages used the easily damaged Federal indicator. The largest models have a convenient lifting lever. To our detriment, Sunnen does not have a distributor network, so you'll have to buy directly from them. Disappointments: some thin-walled moving parts in the head break quickly, and often, and since the manufacturer does not make these parts available, your only option is to replace the entire head. We like the way these gages are designed with a minimum of screws. Assembly is cleverly sequential and if you ever take one apart, carefully remember the sequence or you'll be scratching your head. Although small quantities are usually in stock, the manufacturer makes custom lengths on request and this can take up to 4 weeks.

Teclock

Teclock dial bore gage made in Japan. Models CCI-35, CCI-60, CCI-150, CCI-250 may be available but finding a distributor who carries these is a task for Miss Marple. Some metric versions appear to be available through Amazon. These are cheap bore gages which have the disadvantage that parts (accessories and spare parts) may be impossible to get. Other cheap bore gages exist and if money is your only criterion then you have plenty of options. If you need quality, on the other hand, consider Mitutoyo bore gages or Dorsey mentioned above.

Veribor Light

Veribor Light dial bore gage is made by Tesa, Switzerland, is of European origin. This "light" version was introduced in 2007. It looks like Tesa resurrected an old Etalon design with modifications, perhaps to offset the problems with their costly Compac bore gages. They look pretty much like the Mitutoyo (which was also a copy of the old Etalon design). The centering device is a pair of wheels which some say reduces scratching or marring of polished surfaces. A major difference between the Veribor and other bore gages is the Veribor will take any dial indicator or probe, without having to use a special housing. The complete set ranging from .7" to 6.0" is a pretty good deal since these are currently being offered at an introductory discount. Tesa claims that replacement parts will be available.