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Southern Style Thread Ring Gages

The Southern Adjustable Style thread Ring Gage features an adjustment mechanism that maintains the roundness integrity of the gage throughout its use. The helix path of the thread along the line of adjustment remains true and in alignment throughout the life of the gage. Aluminum gage bodies anodized green for Go and red for NoGo provide easy identification. Precision ground thread inserts are made of oil hardened tool steel. Thread class and tolerances conform to ASME/ANSI B1.2 or B1.16M. Sizes below .2500 and M6 are counterbored to hold specific length.

Southern Style Thread Ring Gages


Blunt Starts, Higbee Cuts, and Depth Notches

Thread Check can add many custom features to our thread gages such as depth notches, blunt starts, blunt points or chamfers that are
beneficial for several applications including thread depth gaging and short or shallow threads

Blind Hole – A hole that goes partially through a part.


Blunt Point –The removal of a male center point from threads smaller than #6 (M4).
This does not allow the gage to be face ground to within .5P.
This is not a Blunt Start. See Convolution below.


Chamfer – An angle ground on the front of a gage that allows for easier assembly with the mating part


Convolution – Removal of the incomplete thread back to the first full thread. Also
known as a “Blunt Start” or “Higbee Cut” per ASME B1.7 – 2006


Depth Notch – Measure from the centerline of the first full thread to the flat step of the notch.
A depth notch is only used on a go plug gage and is used to measure thread depth.


Grind Face w/in .5P - A convoluted thread plugs face is ground back to the base of
the first full thread. This permits the gage to inspect a blind hole to the bottom of the thread.

Contact Thread Check Inc for more information

800 767 7633 or 631 231 1515



New Digital Depth Thread Gages

Measure thread depth and gage thread size at the same time. Thread Check's digital thread depth gage uses ANSI standard taperlock thread plug gages for fast and accurate thread depth and size control. Thread Check's Thread Depth Control Instrument digitally measures thread depth with a resolution of .0005"/.01mm and accuracy of .002"/.05mm.

  • The gage is available in 4 handle sizes for diameters from .164" to .8125"
  • The No Go gage is conveniently located on the opposite end of handle
  • It's also Ideal for use with cylindrical plug gages for measuring the depth of plain bore holes
  • Available with optional wireless data interface to send dimensions into a PC
  • Custom gages, special length, special depth stops, dirt and air grooves are priced on request
  • LCD display with preset function
  • No Go gage conveniently located on opposite end of handle
  • Gage internal threads and accurately measure thread depth at the same time
  • Ideal for use with cylindrical plug gage for measuring bore depth
  • Thread Check's Thread Depth Control Instrument digitally measures thread depth with a resolution of .0005"/.01mm and accuracy of .002"/.05mm
  • Compatible with ANSI standard taperlock thread and plain gages in chrome and steel
  • Easy depth setting with optional master setting gage
  • Reading scale is always visible as gage rotates
  • Depth scale can be fixed for minimum thread depth

Visit our website or contact our sales department for more details


Digital Depth Thread Gage



Thread Check Inc. launches new site at

Thread Check Inc has launched its new web site

The new Thread Check website is a responsive web design.

Thread Check’s new website will enhance our customers experience with our products and service and make a powerful impression on our industry. Our goal for is to create an engaging site with detailed product and technical information.

Responsive web design (RWD) is an approach to web design aimed at crafting sites to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices from desktop computer monitors to tablets and mobile phones.




Gear Measuring Wires

Thread Check's gear measuring wires are used to check the tooth thickness of gears at the pitch diameter. The gear wire method is more accurate than using tooth verniers to measure the tooth thickness. A measurement over the wires using a micrometer is compared with a perfect gear which is obtainable from the Van Keuren Handbook No 37. The Van Keuren Gear Measurement Tables are accurate to .0001" for 1 diametral pitch gears. A value based on the selection of pressure angle, number of teeth, and wire size is divided by the diametral pitch of the gear being measured. If the actual measurement is larger than the table value then the teeth are thick. If the value is smaller then the teeth are considered thin. A copy of the Van Keuren Handbook can be purchased on line at

Thread Check's gear measuring wires are supplied in sets of 2 identical wires. Thread Check's gear measuring wires meet or exceed Federal Specification GGG-W-366B for Grade AMGW. Wires are lapped  to RMS micro inch finish or less. Contact Thread Check Inc for modified gear wires, carbide gear wires, flatted gear wires.
Thread Check offers Gear measuring holders for both 2 and 3 wire gear applications. Please provide measuring instrument and spindle diameter when ordering.


UNR Screw Thread Form

The UNR thread was developed for fatigue resistant safety critical fasteners during the 1950s.

The UNR thread form applies only to external threads. Its design form is the same as that of the external UN thread except that the root is required to be rounded. UNR threads are applied most often to high volume commercial fastener threads produced by rolling

Per ANSI/ASME B1.12003 – paragraph 2.3.1: “The rounded root (UNR Thread)…reduces the rate of threading tool crest wear and improves fatigue strength over that of a flat root (UN) thread.”

Thread Designations:

UN = Basic Unified National thread series
UNR = Basic Unified National thread series with external thread controlled root radius
UNS = Special Unified National thread series
UNRS = Special Unified National thread series with external thread controlled root radius
UNC = Unified National Coarse thread series
UNRC = Unified National Coarse thread series with external thread controlled root radius
UNF = Unified National Fine thread series
UNRF = Unified National Fine thread series with external thread controlled root radius
UNEF = Unified National Extra Fine thread series
UNREF = Unified National Extra Fine thread series with external thread controlled root radius

External UNR threads per ANSI/ASME B1.1
paragraph 1.3: UNR threads have "a rounded root contour" at the minor diameter.
paragraph 2.3.1(a): "The root contour ... shall have a smooth, continuous, non-reversing contour with a radius of curvature not less than 0.10825318P at any point and shall blend tangentially into the flanks and any straight segment. At the maximum-material condition, the point of tangency shall be at a distance not less than 0.625H below the basic major diameter.”

For internal threads there is no UNR requirement. Use a standard UN thread plug gage.


The difference between a UNR and UN thread ring gage is marking only. The thread ring gages are identical. Although Thread Check Inc. can mark thread ring gages with the R designation, it is not a standard requirement. Use the same ring gages to check either the UNR or UN screw thread form. The amount of radius at the root of the UNR thread form is too small to require a modification of the standard UN thread form ring gages.


UNR Inspection Method for External Root Radius:

  • Optical Comparator or Vision System
  • Tri Roll thread comparator with minor diameter type 7 rolls ( 55° included angle ). The Tri Roll thread comparator may be more practical in a high volume production environment


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Master Thread Plug and Ring Gages for Thread Comparators

Master Setting Plugs For Tri Roll Thread Comparators

Class "W" Full Form Master Setting Plugs gages are used to set Tri Roll Thread Comparators. Master Thread Setting plugs are manufactured to a go basic pitch diameter size. PITCH DIAMETER is the theoretical diametrical plane which passes through a thread at the point where the width of the thread tooth and groove are equal. The pitch diameter is measured by means of the universally recognized three wire method.


Master Setting Rings For  ITC-Internal Thread Comparators

Class W tolerance master setting ring gages are used to set ITC – Internal Thread Comparators. Class W tolerance master setting ring gages are manufactured to a go basic functional diameter. FUNCTIONAL DIAMETER is the actual (measured) pitch diameter of a thread adjusted by the cumulative effects of lead error and angle error, which is always added to external threads and subtracted from internal threads.

master setplug thread comparator
master set ring ITC comparator


BSB Threads – British Standard Brass

BRASS THREADS (British Standard Brass)

BSB - Brass threads are used for brass tubing with a uniform wall thickness regardless of the tube diameter. 26 Threads per inch is the standard on all tube diameters.

The reason for using 26 tpi, is brass tube has a almost the same wall thickness irrespective of the outside diameter of the tube, therefore as BSW thread depths are determined by the threads per inch, a lower tpi would reduce the strength of the tube or cut right through it.

The included thread angle on all BSB threads is 55 degrees

Nominal sizes range from 18 to 2 inches.
Thread Check supplies a complete range of thread gages.

Thread Form Data Tapping Hole
Diameter O/D Core Pitch Depth Radius Effective Dia T.P.I Dec / Met / Frac
1/8" 0.125 0.0757 0.03846 0.0246 -- 0.1020 26 Number 47
1/4" 0.250 0.2007 0.03846 0.0246 -- 0.2254 26 Number 6
3/8" 0.375 0.3257 0.03846 0.0246 -- 0.3504 26 Letter Q
1/2" 0.500 0.4507 0.03846 0.0246 -- 0.4754 26 29/64"
5/8" 0.625 0.5657 0.03846 0.0246 -- 0.6004 26 37/64"
3/4" 0.750 0.7007 0.03846 0.0246 -- 0.7254 26 45/64"
7/8" 0.875 0.8257 0.03846 0.0246 -- 0.8504 26 53/64"
1" 1.000 0.9507 0.03846 0.0246 -- 0.9754 26 61/64"
1-1/8" 1.125 1.0757 0.03846 0.0246 -- 1.1004 26 1-5/64"
1-1/4" 1.250 1.2007 0.03846 0.0246 -- 1.2254 26 1-13/64"
1-1/2" 1.500 1.4507 0.03846 0.0246 -- 1.4754 26 1-29/64"

BSB Threads - British Standard Brass

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ISO 9001 Certification

On July 30th of 2014, ABS Quality Evaluations conducted a 1 day audit of Thread Check Inc. There were no major or minor non conformities found during the audit. This is the 5th year in row with zero nonconformities. This is a testament to our organization's commitment to customer satisfaction, employee empowerment and continuous improvement.


Thread Measuring Wire Calibration

Reference ASME B89.1.17-2001

Attributes to be inspected

  • Diameter – Use high magnification comparator or measuring instrument with adjustable measuring force.  .0000020” resolution or better is required. Use a cylindrical anvil.


  • Roundness – Use Vee anvil with 60 degree included anvil. Cylindrical masters and a normalizing plate are required.


Suggestions for improved accuracy

Calibrate only in the central middle half of the thread measuring wire.

Thread measuring wires are calibrated on a functional basis so as to compensate for deformation when the wires are being used.

  • Wire diameter is measured with the wire placed over a cylindrical anvil of a known size by a flat round contact point.
  • The effects of errors in roundness are determined by noting the changes in diameter measurement utilizing a vee anvil and taking measurements around and along the wire.

Refer to ASME B89.1.17-2001 for measuring force and contact point configurations.

Wires must be unrestrained during measurement. They should be held in place by the specified measuring contact force only.

The set of 3 wires in a set must be calibrated at the same time to ensure the commonality of size standard is met. Each wire in a set must have the same diameter within .000010”.

Handle all thread measuring wires with care. Wires should be handled with soft tip tweezers

Allow adequate time for thread measuring wires to normalize. Use a normalizing plate adjacent to the measuring equipment.

Measurement Uncertainty

Attribute Normal Laboratory Conditions Optimum Laboratory Conditions
Wire Diameter 0.000025”/ 0.00064mm 0.000015”/ 0.00038mm
Wire Straightness/Roundness 0.000015”/0.000383mm 0.000005”/0.000130mm



Thread Check Inc.