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Compac Test Indicator Contact Point
Genuine MTC contact points with stainless steel bodies

We also have contact points for the following indicators:

  • Bestest indicator contact points
  • Compac M1.6 carbide and ruby test indicator contact points … see information on this page
  • Interapid M1.7 carbide, ruby and Teflon contact points
  • Mitutoyo test indicator contact points
  • Starrett test indicator contact points
  • TesaTast indicator contact points
  • contact points for dial indicators

Compac M1.6

 

How are Compac test indicator contact points measured? From the end of the thread to the center of the ball. Thread size is M1.6

Carbide .080" (2 mm) contact points come standard with new indicators. They are highlighted in the section below.

Model

Length

Ball Diameter

Price

Our Ordering Number

Manufacturer Equivalents

214A + 214GA
215A + 215GA
224A + 224GA
225A + 225GA
234A + 234GA
235A + 235GA
245A + 245GA

.72"

.015" carbide

$21.50

MTC25-01 buy now

none

.031" carbide

$19.50

MTC25-02 buy now

18.66011

.080" carbide

$19.50

MTC25-05 buy now

18.66005

.120" carbide

$19.50

MTC25-07 buy now

none

.040" ruby

$29.50

MTC25-08 buy now

none

.080" ruby

$29.50

MTC25-09 buy now

none

.120" ruby

$29.50

MTC25-11 buy now

none

Model

Length

Ball Diameter

Price

Our Ordering Number

Manufacturer Equivalents

213LA
213GLA
223LA
223GLA
233LA
233GLA

1.44"

.015" carbide

$21.50

MTC25-12 buy now

none

.031" carbide

$19.50

MTC25-13 buy now

18.66024

.080" carbide

$19.50

MTC25-16 buy now

18.66009

Model

Length

Ball Diameter

Price

Our Ordering Number

Manufacturer Equivalents

244A
244GA

.67"

.015" carbide

$21.50

MTC25-23 buy now

none

.031" carbide

$19.50

MTC25-24 buy now

18.66010

.080" carbide

$19.50

MTC25-27 buy now

18.66007

.120" carbide

$19.50

MTC25-29 buy now

none

Model

Length

Ball Diameter

Price

Our Ordering Number

Manufacturer Equivalents

244LA
244GLA

1.65"

.031" carbide

$19.50

MTC26-02 buy now

none

.080" carbide

$19.50

MTC26-05 buy now

18.66008

.120" carbide

$19.50

MTC26-07 buy now

none

Model

Length

Ball Diameter

Price

Our Ordering Number

Manufacturer Equivalents

213 + 213G
215 + 215G
216G
223 + 223G
225 + 225G
233 + 233G
235 + 235G
242 + 242G
245 + 245G

18 mm

0.8 mm carbide

$19.50

MTC26-09 buy now

18.66014

2 mm carbide

$19.50

MTC26-12 buy now

18.66003

3 mm carbide

$19.50

MTC26-14 buy now

18.66021

Model

Length

Ball Diameter

Price

Our Ordering Number

Manufacturer Equivalents

212L
212GL
215GL
222L
222GL
232L
232GL

36 mm

0.8 mm carbide

$19.50

MTC26-16 buy now

18.66016

2 mm carbide

$19.50

MTC26-19 buy now

18.66004

3 mm carbide

$19.50

MTC26-21 buy now

18.66023

Model

Length

Ball Diameter

Price

Our Ordering Number

Manufacturer Equivalents

243L
243GL

45 mm

0.8 mm carbide

$19.50

MTC27-02 buy now

18.66015

2 mm carbide

$19.50

MTC27-05 buy now

18.66006

3 mm carbide

$19.50

MTC27-07 buy now

18.66022

Mercer (Swiss made)

 

Swiss made Mercer test indicators use the same contact points as Compac (shown on this page). You can order any Compac contact point providing the length (L) is the same. Use the chart below to determine the correct length for your particular models.

A word of caution: don't confuse these Mercer model numbers with the Interapid metric indicators, some of which have the same numbers (312-1 for example)! Although the Mercer models are all discontinued, you can still use the Compac points.

Mercer model

Contact Point Length

303-1

.72"

312-1

1.44"

301-1
305-1
306-1

.67"

310-1

1.65"

302-1
304-1
307-1

18 mm

313-1

36 mm

311-1

45 mm

Which contact point to choose?

 

 

Contact points are always available from Long Island Indicator Service. There are four components to take into consideration.

  • ball diameter
  • thread diameter
  • contact point length
  • ball composition

New indicators come supplied with .080" diameter balls as standard. We list the most common sizes below, but for special needs other diameters are often available. Thread diameters vary from manufacturer to manufacturer but are generally metric threads. Manufacturers differ in their method of measuring contact point lengths. It is imperative that the correct length point is used. Refer to the charts below for details on how the length is determined.

What are the contact points made of?

Our contact points are turned from #303 stainless steel and have carbide, ruby, Nylon or Teflon balls.

  • "Alloy 303 is a non-magnetic, austenitic stainless steel that is not hardenable by heat treatment. It is the free machining modification of the basic 18% chromium / 8% nickel stainless steel." [source: pennstainless.com/stainless grades]
  • austenite = a solid solution of carbon in a nonmagnetic form of iron, stable at high temperatures. It is a constituent of some forms of steel. [Oxford English Dictionary]

We recommend carbide balls over chrome or steel for its durability. For special applications you may need the ruby, sapphire, teflon, nylon or some other exotic. Please email special requests.

The contact points listed here are home grown. They're every bit as good as the originals yet they cost less. We give you the manufacturer's ordering number for ease of reference. If you'd rather have the manufacturer's own contact points please send us a request for quotation.

How to install a contact point

Most test indicators come with a little wrench of some sort designed to help you tighten—or loosen—a contact point. Some points have a little hole drilled through them so that you can insert a pin which can then be used to twist the point. Others have two flat spots designed to work with the wrenches supplied. Still others have a hexagonal area which works very well with a pair or small pliers. In all cases, small pliers can be used to remove and tighten contact points. Make sure they are nice and snug, hand tightened only. You don't want to force any contact point that refuses to co-operate. Try another point instead. The thread may be damaged, or you may be using a point with the wrong thread. If the thread breaks off inside the indicator, you may have a hard time getting it out and a repair might then be in order.


Xcelite L4G Sub-Miniature Needle Nose Plier with Green Cushion Grip Handle, Smooth Jaw, 4" Length, 13/16" Jaw Length
 

Cosine error

 

We know that the length of the contact point determines the ratio of leverage. In order to get accurate dial readings the length must be as specified by the manufacturer.

Changing the angle of the contact point changes the ratio just as if you had installed a somewhat shorter point. As a result, the readings on the dial will be higher than they should be.

To compensate for this cosine error it will be necessary to multiply the reading on the dial by the cosine of the angle between the contact point and the measuring surface.

How do you measure the angle? Most of us can intuitively judge an angle of 45° and, perhaps with a little less accuracy, an angle of 30°. Beyond that, we need help. A simple protractor like we used in grade school will suffice. Lay the straight edge on the measuring surface and, by eye, make a judgement of the angle. A few degrees one way or another won't be significant.

Where do you find the cosine? Use a scientific calculator or a printed chart.


Texas Instruments Scientific Calculator

Enter the value of the angle: for 20° enter "20" and press the COS (cosine) button. The display will read .9340 (allowing for rounding up).

Now it's simply a matter of multiplying the reading on your test indicator with this value.

For example: when the reading is .0006" you multiply .0006" x .9340 and the result is .00056"

This is just as expected. Your reading of .0006" was larger by .00004" than it should have been.

From this example you can see that angles of 20 degrees or less have relatively insignificant effects on the reading. But, when the angles are larger you'll be wise to make cosine error adjustments.

This same cosine error applies to all makes of test indicators regardless of contact point lengths and resolutions. Some Fowler test indicators feature "pear-shaped" contact points which compensate, in theory, for the cosine error. These may be a good choice if you frequently use a variety of measuring angles.

 

Ruby, Nylon and Teflon points

 

These contact points are used for special applications, typically in optics. The ruby point outlasts standard chrome points and does not expand or contract with heat and cold. It does not conduct an electric current so it can be used on your machines without creating interference. It is also less likely to scratch delicate surfaces. It's also the material that will hold up to silicon carbide surfaces. The Teflon point is softest made of a solid Teflon ball. It is very white in appearance. It is least likely to scratch but is not as long lasting as the others. The smallest Teflon diameter available is 1/16" (.062"). Smaller points can not be manufactured in this material. The Nylon point is not as soft as Teflon but will last longer. It can also be used where surface damage is an issue. Nylon appears opaque.

If you buy any new test indicator from us, you may request one of these points to replace the standard carbide point. A fee applies to make up the difference in cost.

 

Longer contact points

 

You may wish to substitute a long contact point on short point models. If the point is exactly twice the length then the readings on the dial will be doubled. A .0001" indicator will now read .0002" and a .0005" indicator will now read .001".

The indicators were not designed with these long points in mind and you may see some problems with repeatability and hysteresis because these long points weigh more. The extra weight interferes with the hair spring and return spring and that may be noticeable in .0001" models.

Once this long point is installed, be sure to label the indicator with the new readings so no one else will make mistakes. These double lengths can be custom made for most models, although some are in stock (see charts below).

 

 

From our reference shelf:

The Companion Reference Book on Dial and Test Indicators … page 178
BesTest and TesaTast Indicator Repair Manual … page 177
Starrett 711 Last Word Indicator Repair Manual … page 199
Interapid Indicator Repair Manual …
page 208
Compac Test Indicator Repair Manual ... page 194
 

www.longislandindicator.com

Long Island Indicator Service Inc
14 Sarah Drive — Hauppauge NY 11788 — USA


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This page's most recent revision: 9 MARCH 2017
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