Starrett 657-3 Universal Indicator Holder Arm Assembly for Magnetic Base Indicator Holder

The Starrett 657-3 Universal Indicator Holder arm assembly has a pivoting arm and is designed for use with the Starrett 657-1 and 657-2 magnetic base universal indicator holders. The triple-jointed arm has a 12"working radius and three pivots for positioning the indicator. All pivots are controlled and tightened using one tightening knob. The arm assembly accepts indicators with a 3/8" (9.5mm) stem, a standard dovetail mount, a body clamp, or a 1/4" (6.3mm) or 3/16" (4.7mm) shank. The arm assembly can also be used on the Starrett 659P base (requires 659 thread adapter, not included).

Magnetic bases are magnetic fixtures commonly used in metalworking to hold dial indicators, and are also used in other fields, such as optics. Magnetic bases can assist the user with setting up a workpiece in a milling machine, surface grinder, or other machine tool. The vertical post and rod in a magnetic base connect using swiveling connectors, or snugs. This allows free motion of the arm so that the dial indicator can be moved into position on the workpiece. Many magnetic bases have a V-step, which is a V-shaped notch in the base for holding the base to arbors, shafts, and other cylindrical items. The magnetic base has a circular hole through the center. A round permanent magnet is inserted into this hole, and a handle or button is attached to allow the user to rotate the magnet. Rotating the magnet turns the base on and off as this causes the position of the magnetic field to rotate as well. In the on position, the iron is acting as an extension of the magnet, while in the off position, the magnet is acting as a keeper, preventing the magnetic field from extending through the base.

The L.S. Starrett Company manufactures precision measuring tools, metrology and testing equipment, and saw blade products. The company, founded in 1880, is headquartered in Athol, MA.