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Flex Hole Location Gages

Flexible hole location plug gages also referred to as centerline hole location plugs are used to determine the true centerline to centerline distances of threaded holes. The flexible hole location gage is slotted at 90° increments to ensure positive location on the thread flanks regardless of hole size. This feature provides a firm locating grip without pulling the shoulder of the plug up against the hole face thus avoiding any squareness error being transferred to the centerline measurement. The center is concentric to the threaded section within .0002” TIR for probe location of coordinate measuring machines as well as plate inspection setups as “overpin” measurements. The flexible hole location gage can also be used with vee blocks to check concentricity to other diameters. Thread Check stocks flexible hole location gages in unified and metric sizes. Special sizes and modifications to increase the post length can be priced on request.


Proper Care And Usage Of Gages

Part dimensions to be gaged should be cleaned and burr free to prevent gaging interference. Grit and part chips which become lodged in thread gages will create scratches and wear on the flanks of threads and on the outside and inside diameters of cylindrical plain gages. Various materials such as aluminum and castings are extremely abrasive and will tend to wear out gages more quickly than other types of materials. Finer pitch and smaller diameter thread gages tend to wear quicker than larger and coarser pitch gages and have less gage tolerance as well. Regarding thread gages, it only takes a small amount of wear to have a significant effect on the pitch diameter. The wear on each flank angle is multiplied by almost 4 times to determine the total impact of wear on the pitch diameter. 50 microinches or 1 micron of wear per thread flank will impact the measured size by .0002” which can be the total tolerance of many thread gages.

Selecting higher precision gagemaker tolerances for cylindrical plug and ring gages will consume less product tolerance and will allow the acceptance of slightly more product but with less gage wear life and greater expense. Thread Check’s engineering staff can make recommendations in selecting the correct gagemaker tolerances for a given application. The normal rule of practice requires that 10% of part tolerance be divided between the Go and the No Go gages. Applying this practice results in gage tolerance always being included in the part tolerance by up to 10%.This could result in the possibility that 10% of good parts may fail inspection but that no bad product would ever pass. Assuming that higher precision gagemaker tolerances are better, is not valid, and may create quality issues as these gages tend to wear quicker with the potential of becoming undersized and passing bad parts.

Gages should be turned or pushed slowly and gently into or onto the dimension being checked. Forcing gages will result in faulty gaging and the possibility of damaging both the part and gage. Spinning thread ring gages or thread plug gages onto or into parts will create greater friction and increased wear thus reducing the life of the gage.

Using hard chrome plated thread gages can extend the wear life by more than 100% over standard tool steel gages which can provide dramatic savings on replacement costs. Thread Check supplies all standard size thread plug gages in inches and metric up to 1 ½ or 39mm in diameter in hard chrome at no additional cost. Other options for coatings and alternate material for thread gages and cylindrical gages include tin coat, carbide, alternate steels and even ceramic. There are pros and cons to utilizing various coatings and materials in gage applications which should be discussed with your gage maker. For example, gages made of carbide and ceramic are extremely durable and have excellent wear properties, but can be extremely brittle and break and chip if not handled carefully.

A thin coating of gage lubricant will help reduce friction from gage to part.

Proper training of personnel involved in the use of gages will pay dividends on ensuring the gages are treated with care and last longer. Review the current inventory of gages and look for visual signs of nicks, dents and scratches on gage members and handles. Evidence of this may suggest the gages are not being handled properly.

The effects of thermal expansion should be taken into consideration on both the part and the gage.

The temperature of the part and the gage should be the same. 68° F is the ideal temperature at which both part and gage should be at when inspected because gages are calibrated at 68° F. This effectively eliminates any error due to thermal expansion.

Protecting gages from excessive heat, humidity, moisture and corrosive chemicals will extend the life of your gages. After use, gages should be cleaned and recoated with a thin-film rust preventative or dipped in an easy to peel oil-based waxed coating, and stored properly.

Gages should be periodically inspected and calibrated to assure accuracy. Go member gages tend to wear quicker with normal use. NOGO gages will wear on the ends that receive the greatest usage. Frequency of inspection and calibration should be dependent on such factors as the amount of usage, part and gage material, tolerance, and quality procedures


The major differences in common thread and cylindrical gage materials and coatings

All standard gages are manufactured from tool steel and hardened to 58 – 62 Rc

Chrome is a plating process that increases the hardness to 70-72 Rc. The Chrome process also reduces friction on the gage and prevents corrosion. There are many variables that effect gage life or wear but chrome can significantly extend the wear life of a gage by more than 100%. The typical cost to add chrome is usually 30% more than tool steel.

Carbide is a sintered metal with a harder but more brittle surface than chrome. The RC of carbide gages is 79-81 Rc.

Titanium Nitride (TiN) is a general-purpose coating for corrosion resistance and increased tool life. The Rc is approximately 85RC

When selecting alternate materials to tool steel it is important to consider the benefits to the additional cost.


A New Power Driven Thread Gage

Multimatic Products recently developed a power driven thread gage to safely drive standard AGD go thread plug gages at a fraction of the price of some other types of units manufactured overseas in Germany. The power driven thread gages have been fairly popular in the automotive manufacturing industry for many years. The Rotary Thread Inspection Tool as Multimatic Products refers to it also checks thread dept up to approximately .7500 inches.

I have had the opportunity to work with the unit and the claims stating “reduced operator fatigue” are well founded in my opinion. I performed inspection on several hundred small .3125 inch coupling nuts and the tool performed soundly. The coupling nut featured a .250-36 UNS 2B thread with a thru hole depth of .3125. The gage powered through the part smoothly and then automatically reversed direction when it reached its thread depth.  The gauging process was very simple and required no continuous hand turning. Conventional gauging would have required 11 turns of the standard thread plug gage into the part and then 11 turns to turn the gage out for a total of 22 turns per part. That adds up when inspectors are checking over 3000 parts per month or more!

I think this may be a ideal gauging solution for many companies and welcomed relief for the quality control inspectors.

For more information you can visit


White Paper on Resolving Measurement Disputes

Disputes over measurements can be costly for both parties to resolve and may hinder ongoing relations between suppliers and users of gages and instruments. Often it is simpler for both parties to agree to accept an average value of their readings as the final ‘size’ or the point at which their readings plus measurement uncertainties overlap.

The obvious way to avoid such problems is to agree beforehand on a method that will be used to resolve them if they arise. Often, the degree of separation between the readings dictates the best approach to take. Where the uncertainty of each party is significantly different, the party with the lowest uncertainty in the calibration would be considered more reliable.

The AMTMA offers the following methods as options you can choose from. If the Referee Method fails to bring a resolution, then the Universal Standard Method should be used due to the fact it is technically based and internationally accepted by metrologists in all disciplines.

The Referee Method

The two parties agree on a third party to provide a referee measurement that it is agreed will be considered as the actual value. An alternative on this is where the reading by either party that is closest to that provided by the referee is considered the accepted dispute.

Unless otherwise agreed to, the costs of using laboratories in this method are paid by the losing party.

The Unviersal Standard Method

National and international standards agencies have produced methods of resolving measurement disputes that focus on the uncertainty budgets of those that have produced measurements. The advantage of this method is that its technical base tends to remove personalities from the equation and may indicate that neither party to a dispute has the capability required to resolve it.

Using this method, the onus of proving a measurement falls on the party who has questioned the results of calibration. If requested, this party must provide a copy of their uncertainty budget for the measurement to the other party review. Budgets from both parties should be compared. Such a review should focus on seeking agreement between both parties respecting each element included in the budget since it will rarely, if ever, be all right or all wrong. The mathematics should take care of the rest. There may be cases where one or more elements have not been included in the budget included in the budget and when they are, the outcome changes significantly.

In the event one or more assumptions in the budget cannot be resolved, a third party can be asked to provide an opinion on them.

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The difference between taperlock style and reversible style thread plug gages

The taperlock thread plug gage style allows for a quick and convenient replacement of the gage member into an existing handle. A worn gage member can be simply removed and a new replacement inserted into the handle.

The reversible thread plug gage style allows for one end of the gage to be rotated so the user gets two gages in one. A worn gage end can be turned around by simply opening the collet of the handle and turning the gage and bushing around so the opposite end essentially becomes a new gage. The reversible thread plug gage is ideal in high volume inspection applications.

Both Thread Check’s reversible and taperlock style thread plug gages are manufactured per ANSI/ASME B1.16M ( metric ) or ANSI/ASME B1.2 ( inch ). Both styles of thread plug gages are manufactured to an X tolerance. Both styles are available in M, MJ , UNC, UNF, UNEF, J and specials. Reversible and taperlock style thread plug gages are stocked in hard chrome coating which extends the wear life of the gage by more than a 100% thus providing dramatic savings in replacement costs. All Thread Check, Inc. gages are manufactured to the high end of the tolerance to ensure longer gage life. Thread Check, Inc. manufactures both taperlock and reversible style thread plug gages in carbide, ceramic and other types of specialty steels. Thread Check manufactures many types of special gages including pre-plates, multiple starts, special leads, acme threads, buttress threads, square threads, extra length thread gages, and custom gages to print. All thread plug gages are traceable to N.I.S.T.

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