The primary function of the sliding strip or rod found at the back of a slide caliper is for measuring depth.
Slide calipers, often known as Vernier calipers, are versatile measuring tools. While the main jaws are used for measuring external and internal dimensions (distance and diameter), the specific component at the rear— variously called a depth rod or depth gauge — serves a distinct purpose. As highlighted by the reference, "The strip at the back of Vernier caliper is used for measuring depth of a cylinder." This indicates its primary application, though it is used for measuring the depth of any hole, cavity, or step.
How the Depth Rod Works
The depth rod is attached to the movable jaw of the caliper and extends out from the end as the jaws are opened. To measure depth:
- The end of the caliper body (the fixed part) is placed across the opening whose depth is to be measured.
- The movable jaw is then extended until the tip of the depth rod touches the bottom of the hole or cavity.
- The depth is then read directly from the main scale and the Vernier (or digital) scale on the caliper, similar to how external or internal measurements are taken.
Applications of the Depth Rod
This specific function allows for precise measurements in various scenarios:
- Hole Depth: Measuring the depth of drilled or bored holes.
- Recess Depth: Determining the depth of cutouts or recesses in a workpiece.
- Step Height: Measuring the height difference between two surfaces.
- Blind Holes: Essential for measuring the depth of holes that don't go all the way through a material.
| Caliper Part | Primary Function(s) |
|---|---|
| External Jaws | Measuring outside dimensions (length, diameter) |
| Internal Jaws | Measuring inside dimensions (bore diameter, slot width) |
| Depth Rod/Strip | Measuring depth (of holes, steps, cavities) |
| Main Scale | Reading the primary measurement |
| Vernier/Slide Scale | Reading fractional parts of the measurement for higher precision |
The "jaws and metallic strip," as mentioned in the reference, collectively form the key measurement elements designed for various types of dimensioning, making the slide caliper a comprehensive tool for length, diameter, and depth measurements.
