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How to Use a Hermaphrodite Caliper

Guide · Updated October 28, 2026

A hermaphrodite or odd-leg caliper has one bent leg with a heel that rides along an edge and one straight leg with a scribing point. It scribes lines parallel to an edge and finds the center of bar stock quickly. It is a rough layout tool, good to about 1/64 in, and much faster than setting up a height gage.

Precise layout

For layout within a thousandth or two, use a height gage set with gage blocks on a surface plate. The free Gage Block Calculator builds the stack.

Step by step

Sharpen the scriber: A sharp, conical point gives a fine line; touch it up on a stone.
Set the distance: Hang the heel on the end of a steel rule and set the point on the graduation you need; read with a loupe.
Dye the part: Apply layout dye and let it dry.
Ride the edge: Keep the heel firmly against the reference edge, legs perpendicular to the edge.
Scribe in one pass: Pull the caliper toward you along the edge with light even pressure, tilted slightly in the direction of travel.
Find centers: On bar ends, scribe arcs from three or four points around the edge; the center is in the middle of the small figure they make.
Prick punch and check: Prick punch the intersection, then measure from the edges with a rule.

Worked example

Centering the end of 1.000 in square bar. Set the caliper close to half: 0.500 in. Scribe from all four sides. If the setting is exactly half, the lines meet at one point. If it is 0.510 in, opposite lines cross past center and form a small square 2 × 0.010 = 0.020 in across; if it is 0.490 in, they fall short and leave a 0.020 in square the other way. Either way the true center is the middle of that small square. Measure the square with a rule: 0.020 in tells you the setting was 0.010 in off, and you can reset to 0.500 in and scribe again. For round bar, scribe four arcs at 90° intervals; the arcs enclose a small curved figure whose center is the bar center.

Accuracy and when to use something else

Setting from a rule and scribing by hand typically holds about 1/64 in (0.015 in). That is fine for rough cuts, weld prep and drill locations that will be spot drilled. For anything tighter, use a height gage on a surface plate or locate on the mill with an edge finder.

Common problems

A wandering line means the heel lifted off the edge or the part edge is rough; file a clean reference edge. A double line means you scribed twice. A setting that changes during use means the joint is loose; tighten the pivot nut. Rounded or chamfered edges let the heel drop and shift the line inward.

Tips

Layout: layout dye and scribing.
Center: center finder for round bar ends.
Height gage: height gage layout for precision.

FAQ

What is a hermaphrodite caliper?

An odd-leg layout caliper with one heeled leg that rides an edge and one scribing leg.

How accurate is it?

About 1/64 in when set from a rule and used carefully.

How do I find the center of a bar?

Set to about half the width, scribe from each side, and take the middle of the small figure the lines make.

How do I set it?

Hang the heel on the end of a steel rule and set the point on the graduation.

What should I use for tighter layout?

A height gage on a surface plate, set with gage blocks.

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