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Simpson Double Machine Screw Anchors (DMSA)

Published by Robert Carlisle on Aug 31st 2008

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Simpson Strong-Tie, Inc. has a division that sells concrete anchors called Simpson Anchor Systems®. Their double expansion anchor is sold as the DMSA machine screw anchor - an acronym for double machine screw anchor. The DMSA has an expanding cone at each of its two open ends to allow the DMSA to expand the entire length of the anchor and to provide better performance in base materials with questionable strength.

DMSA Federal Specifications

DMSA all meet federal specifications A-A-1923A, Type 3, with an exception made for the 1/4” DMSA25 and the 5/16” DMSA31.

DMSA Base Materials

The DMSA machine screw anchor can be used in a variety of base material, such as concrete, brick or block. In most cases, the DMSA is more versatile than the single expansion anchor SMSA because it can be used in the base material of questionable strength.

DMSA Diameters

The DMSA is a female anchor and its internal threads of the anchor determine the size designation. The DMSA comes in four diameters from 1/4” to 1/2”, and other brands, such as, have diameters of 5/8” and 3/4”. All of the threads on the DMSA are national coarse machine threads and will accommodate any bolt or threaded rod with the same national coarse threads.

DMSA Diameter of Hole

The hole that is drilled in the base material for the DMSA machine screw anchor must be drilled with a hammer drill and a carbide bit that meets ANSI standard B212.15. The diameter of the hole drilled is the same diameter as the outside diameter of the anchor (see chart below).

Depth of Hole

The deeper into the base material the anchor is inserted the better the DMSA holding values may be. The holding values of the DMSA anchor are dependent on the holding strength of the base material. The DMSA must be embedded a minimum distance into the base material. The DMSA machine screw anchor requires that the anchor is inserted the length of the anchor at minimum so that the end of the anchor is flush with the surface of the base material (see chart).

Thickness of Concrete

The thickness of the concrete that the DMSA machine screw anchor is placed into must be no less than 1.5 times the embedment depth of the anchor. If a 3/8” DMSA machine screw anchor is being used then the concrete must be at a minimum 2.44” thick.

DMSA Length of Bolt

The length of the bolt used with a DMSA anchor must be long enough to engage a minimum 2/3 of the threads on the expansion cone. To determine the overall length of bolt needed, add the thickness of the material being fastened plus the depth of embedment of the anchor.

DMSA Product Information Chart

Item #

Anchor Size

Drill Bit Size

Embedment Depth

Box Quantity


1/4” -20





5/16” - 18





3/8” - 16





1/2” - 13




DMSA Installation Instructions

Caution: Holding values may be reduced if the anchor is placed in a hole that is oversized, which prevents the anchor from being expanded properly.

1. Using a hammer drill, drill a hole into the base material with a carbide bit that meets ANSI standard B212.15. Make sure that the diameter of the bit is equal to the diameter of the hole required for the diameter of DMSA being installed. Drill the hole to a depth of 1/8” deeper than the intended anchor embedment, making sure that the hole depth is at a depth at least equal to the anchor length.

2. Using a vacuum, compressed air or a wire brush, clean out the hole of all debris and dust.

3. Insert the DMSA machine screw anchor into the hole with the threaded cone first. A hammer may be used to tap the DMSA machine screw anchor into the base material until the anchor is at least flush with the surface.

4. Move the hole in the fixture to be fastened over the DMSA machine screw anchor until the holes line up. Insert a bolt through the fixture and into the DMSA machine screw anchor. Turning the bolt clockwise will engage the threads and expand the anchor. Turn the bolt until it is tight against the fixture being fastened. Remember to make sure that a minimum of 2/3 of the threads are engaged by the bolt.

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