These indicators have a very light measuring force: just 0,12 N for .0005" models and 0,25 N for .0001" models.

The indicator is designed to measure with the contact point held at an angle of 12° to the measuring surface. (Some sources list this angle as 13 degrees. The difference is not significant.) This allows you to take measurements down a hole or in a bore.

The .080" diameter carbide contact point is easily replaceable with other diameters (from .015" to .120") and other substances (ruby, teflon or nylon). Under some circumstances, you can even install a longer point. See contact points.

The dial hand makes two revolutions in each direction. The small counter hand keeps track of the revolutions.

The dial has balanced numbering: 0-4-0 (.0001" indicators) and 0-15-0 (.0005" indicators). The right half of the dial features a thin black band which will help identify the plus or minus side when using a mirror.

The novel tapered shape tilts the dial towards the observer. Both Mitutoyo and Starrett have recently copied this design. This makes for easier reading with less likelihood of parallax errors as well as a reduction in glare from overhead lights.

If you need to slip the indicator into an opening then you may be interested to know that the width of the body at the stylus (contact point) is 10,3 mm which is broader than Bestest, Tesatast or Compac.

The holding stem is 4 mm (5/32") in diameter. The stem swivels and is attached to the body, although it can be removed and replaced. Simple instructions for this procedure are available on our Do-It-Yourself page. If you need a holding stem with a different diameter, use one of the following adapters show on our spare parts list:

• An elegant 3/8" adapter fits over the 4 mm stem. Order no. 74.108943
• For metric set-ups, use the 8 mm stem adapter. Order no. 74.108942

The dovetails are hardened metal, screwed onto the body. These can also be removed and replaced. See our spare parts list for replacement parts.

Interapid repair

Long Island Indicator is an authorized repair service for Interapid test indicators.

Top-of-the-line Interapid test indicators are probably the most challenging of all to repair. Absolute cleanliness and the replacement of critical parts is essential to a quality repair. We've been trained by masters in the craft, and having an ample supply of fresh parts directly from the manufacturer are able to return any Interapid test indicator to A-1 condition.

To make things easy, we have fixed repair costs. It's our policy to replace any damaged or worn parts necessary for the full function of the indicator. This way you'll be sure to get an instrument that's as good as new and one you can rely on. And, if you request it, you'll get a short-form certificate of calibration, NIST traceable, for free; after all, when you get your indicator back you need to know that it's accurate. If you pay with a credit card, turn-around is less than a week.

• Professional repair service

Is the indicator damaged beyond repair? If the body is damaged in any way (the front end is squashed, for instance) then we'd have to replace the body and you'd have to pay about $190 for the repair. Not usually worthwhile. If the whole face has come off because it was ripped off - that sounds serious, yet happens regularly - it's probably repairable for the normal cost quoted in the paragraph above.

Do you only need a new crystal installed? We charge $45 and that includes return shipping. Just enclose a check and we'll do a 2-day turn around. To make it easy, print out a packing list.

Sorry, we can't repair old models such as the 310B and 311B series. Parts for these indicators are no longer available. If have one of these, then you've gotten your money's worth since they were discontinued about 40 years ago. If you just bought one on eBay, then you've been had.

Using the correct contact point

While various diameter balls do not affect readings, the correct contact point length is critical. (Refer to model information on this page.) Use only points designed for Interapid indicators. Any deviation will result in reading errors.

When ordering new points, take note of the indicator's model number and decide on the ball diameter you'll need.

• Contact points in carbide, ruby or Teflon

Important calibration information

Unlike other test indicators, Interapid indicators do not have serial numbers on them. Perhaps someday the manufacturer will remedy this situation but for now you'll have to assign your own unique serial number to each indicator if you intend to keep track of their calibration. It's easy to scratch a number into the painted body using a sharp tool. A permanent marker with a super fine point will also work. Do not use an electro-engraver because it creates sparks which have been known to damage the pinions on the gears.

Interapid series 312 test indicators are designed to permit a true reading when the angle between the stylus and the reference surface is 12° as shown in illustration A and B.

In the rare cases when axial measurement is required with the stylus at 0° with respect to the reference surface as in C and D in the illustration, (for instance: small diameter bores) the readings must be multiplied by a factor of 1.022

It also follows that incremental calibration discrepancies can be corrected by adjusting the contact point angle.