Faithfull External Spring Caliper - 75mm (3in)

External spring calipers are used to measure or transfer external dimensions, such as diameters or widths, from a workpiece or drawing.

Ensure the adjustment screw is set precisely and that the caliper legs are parallel to the surface being measured. Transferring measurements carefully is key.

No, these are external calipers. For internal measurements, you would need internal spring calipers.

Regularly wipe clean and apply a light coat of machine oil or rust inhibitor to prevent corrosion. Store in a dry environment.

Treated points refer to the sharpened ends of the caliper legs that have been hardened or treated to make them more durable and suitable for marking precise lines on surfaces.

The primary difference is the maximum measurement capacity. The 75mm model is best suited for smaller, more detailed tasks, while larger models offer a greater measuring range.

The adjustment screw may need lubrication. Apply a small amount of light machine oil to the screw threads and work the screw back and forth.

The treated points may have dulled or become damaged. Inspect the points for wear or damage. For minor dulling, careful sharpening on a fine whetstone might be possible, but significant damage may require replacement.

Clean the rusted areas gently with fine steel wool or a rust remover, then immediately apply a thin layer of machine oil to protect the steel finish. Ensure the calipers are stored in a dry place.

Ensure the adjustment screw is tightened sufficiently to hold its position. Check that the legs are fully closed and parallel when set to zero, and that the bow spring is providing even tension.