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Definitions for Concrete Fastener Terminology

Published by Robert Carlisle on Oct 31st 2009

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When working with concrete fasteners and anchors, it is important to understand the terminology used. Understanding the terms used in the installation of these anchors will help you correctly and safely install the concrete fasteners needed for your application. Below is a list of terms and definitions that will help you when working with these anchors.

Anchor spacing- the distance from centerline to centerline between two anchors

Base material- the concrete, brick or block material into which an anchor is placed

Concrete breakout- anchor failure from the deepest embedment of the anchor to the surface of the base material at an angle of about 35 degrees; referred to as the cone of concrete because the breakout with be triangular shaped or cone shaped

Concrete screw- Tapcon® brand concrete screws that are made from carbon steel and the threads are hardened to allow them to tap base material such as concrete, brick or block. The threads are an alternating high/low design with diamond cut notches. Tapcons are plated with a Climaseal® coating for excellent rust resistance.

Critical spacing- the required distance between anchors to meet the maximum holding values

Critical edge distance- the required distance from an unsupported edge of concrete to meet the maximum holding values

Displacement controlled expansion anchor- anchors that are expanded by driving a nail into the anchor body

Drop-in anchor- created from two pieces of tubular steel shield and a cone-shaped expander plug. The shield is threaded for one-half of the length of the interior portion of the anchor, the other half of the anchor is slotted. The slotted portion of the anchor is where the case hardened cone-shaped expander plug is positioned.

Double expansion anchor- the double expansion anchor is made up of five parts: a cone-shaped expander nut, a hollow cone, outer body and two spring bands. The spring bands hold all the anchor parts together into one preassembled single piece and are made from zinc-plated steel. The hollow cone and cone nut are the same except that the cone nut has internal threads and are made from Zamac material. The outer body is tubular and made from die-cast zinc alloy Zamac.

Edge distance- the distance from centerline to centerline of an anchor from an unsupported edge of the base material

Lag shield anchor- comes in two lengths (short and long) and are made up of two parts that are preassembled. The interior part of the anchor is threaded to accept lag screw threads. The outer part is ribbed from the bottom of the anchor to three-quarters up the length of the anchor body. Lag shields are made from a Zamac material that is rust resistant.

Machine screw anchor- machine screw anchors are made up two parts: the internally threaded cone and the outer sleeve. The outer sleeve is made of a rust-resistant material called Zamac. The internally threaded cone is made from zinc plated low carbon steel.

Metal hit anchor- the metal hit anchor or hammer drive anchor is a die-cast anchor consisting of a cylindrical zinc alloy body and zinc plated steel pin expander. The body is split for a major portion at the opposite end the pin expander is inserted. The anchor body is hollow for the entire length to allow space for the pin expander. The pin expander is made from heat treated, high carbon steel that is zinc plated.

Minimum edge distance- the minimum distance to not spall the concrete when anchor is expanded

Minimum spacing- the minimum distance from centerline to centerline for the anchor expansion forces not to overlap; rule of thumb is 10 anchor diameters

Minimum embedment- the minimum distance that an anchor should be placed in the base material to achieve holding values

Nylon nail-its- the body of a nylon nailit is made from a polyamide resin thermoplastic mold injected material, the steel pin expander is a low carbon zinc plated steel. The body is hollow, one end is split and the other end has either a mushroom head, round head or flat head. The steel pin expander has threads on the pointed end and the head is slotted to accept a screwdriver.

Single expansion anchor- this anchor is made of three pieces that are preassembled. The anchor body is made from Zamac, a die-cast zinc alloy. The internal lugs are a cone shaped nut. A spring band made from low carbon steel and zinc plated holds the anchor body and internal lugs together.

Sleeve anchor- this anchor is made up of four parts: nut, washer, threaded stud and sleeve. The threaded stuff is flared to a cone shape at one end and the rest of the stud is threaded. The sleeve is a tubular piece of steel that fits over the stud and expands when the stud is pulled up through it. These anchors come fully assembled and ready to use.

Split drive anchor- the anchor that is all steel, one piece available in two head styles- flat countersunk and round. These anchors are made from heat-treated carbon steel and are thoroughly hardened. At the opposite end of the head, the anchor is sheared into two pre-expanded halves.

Strike anchor- a displacement controlled expansion anchor. The body is steel with a hole down the interior length of the anchor. The hole is smaller in diameter at the opposite end of the threads where the slots are. One end of the anchor is threaded for a portion of its length and the opposite end has four equally spaced slots. A hardened nail is inserted into the interior hole in the anchor and is used to expand the slotted end of the anchor.

Unsupported edge- is where the concrete ends, the sides of a slab of concrete of column of concrete

Wedge anchor- made of a steel rod that is threaded on one end and the other end has a diameter necked down for a short distance that tapers outwardly to the full diameter of the rod. A clip is permanently preassembled in this space.

Depending on your specific application, these terms can help you correctly and safely use concrete anchors to fasten a fixture to a variety of base materials including concrete, brick, and block.

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