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end MeAsurInG rods

precIsIon end MeAsurInG rods And Unless otherwise noted under the individual tools, all have
these features:
InsIde MIcroMeters
The following pages show our varied line of precision end measuring rods • Balanced design for better feel and accurate measurement
and inside micrometers. The variations are fixed-range or adjustable-range • All contact points are hardened and ground for better
micrometers and solid or tubular measuring rods. accuracy and long life
• Satin chrome finish on all micrometer heads and
reading surfaces that resist rust and also make for
easy reading by providing a no-glare background for
the sharp lines and figures
824B • Hardened and stabilized spindle for accuracy and long life
128 • Advanced sleeve design with staggered lines and MicroMeters
distinct figures for precise and easy readability
• Quick and easy adjustment
234A-4
• Starrett workmanship
• Inside Micrometers 121, 124, 823 and 824 by design
have a firmer rotation than regular micrometers. This
is to limit the tendency of the micrometer head to
rotate when withdrawn from the workpiece.

701A

124AZ

MeAsurInG tIps for InsIde MeAsureMents
Whether to use a two-point or three-point contact measuring tool is usually a matter of preference, but there are some differences.
A two-point contact rod-type inside micrometer shown in this section is usually lighter, easier to handle, and more versatile over long ranges from
approximately 6-107" (150-2700mm). Any two-point contact micrometer, regardless of range, can probe a hole better to find the geometry of
that hole than a three-point contact.
Most three-point contact tools have setting rings to ensure accuracy. If you desire very close tolerance work with two-point contact inside
micrometers, it is recommended that they be set to a ring gage or to an outside micrometer.
A three-point contact micrometer shown in the Bore Gages section has an advantage in that it can be seated in position more quickly than a
two-point contact tool. Usually these tools can also be read to a finer accuracy. The three-point tool will tell the maximum true diameter that can
enter the hole a little faster than a two-point contact tool.
Micrometer heads used in these tools are accurate to ±.0001" or 0.002mm, but overall accuracy on tools that add rods is dependent on good
practice and technique.
To ensure accuracy, these practices should be followed:
• Always make sure that there are no specks of dirt between the clamping surfaces of the rods and micrometer heads
• Tighten all rods uniformly, not too tight, not too loose, but a fairly firm assembly
• Assemble long sections vertically or, with support, horizontally
• Because temperature can affect long rods used in these tools, they should be assembled in the same environment in which they will be used
For additional information, refer to the Bore Gage Section.

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