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Starrett 657AA Magnetic Base Complete Set with Base, Upright Post, Rod, Attachment, and Two Snugs

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Specifications for this item
Number of Items
External Testing Certification
Part Number
Item Weight
2 pounds
Brand Name
1 year

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Key Features

  • Compatible with Starrett test, back-plunger, dial, AGD, and miniature-dial indicators, as well as similar indicators from other manufacturers
  • Includes magnetic base, upright base post, two snugs, rod, and indicator attachment
  • Push-button on/off switch for one-handed operation
  • Grips horizontally, vertically, and upside down for versatility
  • Upright base post has overall length of 7-7/16" length, with an adjustable 6" long rod

Package Details

Shipping Weight: 2.05 pounds
Package Size: 10.3 x 2.9 x 2.2 inches

Product Description

Starrett 657AA Magnetic Base indicator holder is an all-inclusive kit for use with all Starrett test, back-plunger, dial, AGD, and miniature-dial indicators, as well as similar indicators from other manufacturers. The set includes a Starrett 657P magnetic base, a 657G upright base post, a 657S snug, a 657X rod, a 657Y indicator attachment, and a PT18724 snug.

The 657P magnetic base is 1-15/16” x 1-5/8” x 1-7/8” (50 x 40 x 48 mm) and has a push-button on/off switch for one-handed operation. The base has three precision-ground, magnetic contact points to grip horizontally, vertically, and upside-down. The 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. The base post is 3/8” (9.5 mm) in diameter and 7-7/16” (190 mm) long. The Starrett 57S and 58S snugs may also be used with this post (sold separately). The 657S snug has two 1/4” (6.3-mm) diameter holes and adapts the 196, 650, and 651 series dial indicators and the 657Y indicator attachment to the 657X rod. The 657X rod is 1/4” (6.3 mm) in diameter and 6” (150 mm) long. It accommodates the Starrett 708, 709, 811, and 711F series dial test indicators. The 657Y indicator attachment has a 1/4” (6.3-mm) outer diameter hole on one end, while the other end is threaded to fit the backs of all AGD indicators (Starrett series 81, 25, 655, and 656) and series 80 miniature indicators. The PT18724 snug has a 3/8” (9.5 mm) diameter post hole and a 1/4” (6.3-mm) diameter gripping hole to accommodate the 657X rod.

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 was founded in 1880, originally manufacturing bench vises, squares, and other tools. They acquired other companies throughout the years, expanding their services into making precision measurement instruments and tools, such as calipers, micrometers, saw blades, and gauges. Starrett is headquartered in Athol, Massachusetts and has manufacturing facilities in Brazil, the United Kingdom, China, and other locations.

What’s in the Box

  • No. 657P Magnetic Base
  • No. 657G Upright Base Post
  • No. 657S Snug
  • No. 657X Rod
  • No. 657Y Indicator Attachment
  • No. PT18724 Snug

From the Manufacturer

Test Indicators cannot be used without proper holders. The 657AA is for use with all Starrett Test, AGD, Dial and Minature -Dial Indicators. Also accomodates similar indicators of other manufacturers.

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