Plunger Dial Indicator

Probe indicators or also called plunger indicators typically consist of a graduated dial and needle driven by a clockwork (thus the clock terminology) to record the minor increments, with a smaller embedded clock face and needle to record the number of needle rotations on the main dial. The dial has fine gradations for precise measurement. The spring-loaded probe (or plunger) moves perpendicularly to the object being tested by either retracting or extending from the indicator's body.

The dial face can be rotated to any position, this is used to orient the face towards the user as well as set the zero point, there will also be some means of incorporating limit indicators (the two metallic tabs visible in the right image, at 90 and 10 respectively), these limit tabs may be rotated around the dial face to any required position. There may also be a lever arm available that will allow the indicator's probe to be retracted easily.

Mounting the indicator may be done several ways. Many indicators have a mounting lug with a hole for a bolt as part of the back plate. Alternately, the device can be held by the cylindrical stem that guides the plunger using a collet or special clamp, which is the method generally used by tools designed to integrate an indicator as a primary component, such as thickness gauges and comparators. Common outside diameters for the stem are 3/8 inch and 8mm, though there are other diameters made. Another option that a few manufacturers include is dovetail mounts compatible with those on dial test indicators.

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