Starrett 657P Magnetic Base indicator holder is compatible with indicators from Starrett and other manufacturers, has a push-button on/off switch, a V-step, grips three ways, and measures 1-15/16 x 1-5/8 x 1-7/8 inches/50 x 40 x 48 mm (H x W x D). (H is the vertical distance from lowest to highest point; W is the horizontal distance from left to right; D is the horizontal distance from front to back.) The base has three precision-ground, magnetic contact points to grip horizontally, vertically, and upside-down, and a push-button on/off switch for one-handed operation. A V-step holds the base to arbors, shafts, and other cylindrical items. The base has an additional 1/4-20 tapped hole on one side for mounting the post. The magnetic base has a non-skid, black wrinkle finish on all non-working surfaces. For use with all Starrett test, back-plunger, dial, AGD, and miniature-dial indicators, as well as similar indicators from other manufacturers.
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 was founded in 1880 and is headquartered in Athol, MA.