Precision End Measuring Rods and Inside Micrometers The following pages show our varied line of precision end measuring rods and inside micrometers. The variations are fixed-range or adjustable-range micrometers and solid or tubular measuring rods. Unless otherwise noted under the individual tools, all have these features: • Balanceddesignforbetterfeelandaccuratemeasurement • All contact points are hardened and ground for better 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 • Hardened and stabilized spindle for accuracy and long life • Advanced sleeve design with staggered lines and distinct figures for precise and easy readability • Quick and easy adjustment • 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 This is to limit the tendency of the micrometer head to rotate when withdrawn from the workpiece. 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. End Measuring Rods 824B 128 234A-4 701A 124AZ 77 M icrometers