Lead anchors can be referred to as lead anchors because they have been manufactured from lead, although not recently due to environmental issues and the use of improved materials. All anchors that are referred to as lead anchors are manufactured by casting parts and then combined into the final product. Today most of the lead anchors are manufactured from a product called Zamac 7. This material is easily poured into molds, are rust resistant and environmentally safer.
First Lead Anchors
The first type of lead anchor utilized lead tape. Once the hole was drilled in the concrete then the lead tape was cut off a roll to be inserted tightly in the hole. A sheet metal screw was then inserted into the hole and turned clockwise, pushing the lead tape outward and holding the screw tight in the hole. This method worked well and gave excellent holding values if done properly. The problem with this method was that the holding values were inconsistent from hole to hole and from installer to installer. However, the principals applied to the lead tape have remained the same for all expansion type anchors used today.
Why Lead Was Used
Concrete fasteners were made from lead because it was easily melted and poured into molds. Once in a solid state, the lead would be pliable and soft. It could be formed to fit the contour of the base material, and be shaped and expanded.
Principles of Lead Anchors
The basic principle of the lead anchors is to drill a hole, then fill it with more material than was taken out. This creates expansion forces, friction and, ultimately, holding values. The evolution of the lead type anchor has led to fasteners that are easily manufactured and that provide excellent, consistent holding values in a variety of base materials. Most of the modern type of anchors can be used in solid concrete, brick, block or mortar joints.
Styles of Anchor
Most of the anchors that are referred to as lead anchor are female anchor, i.e. designed to have a threaded fastener inserted into them. The principle behind the female anchors is to allow the screw to expand the anchor as the screw is inserted. One type of anchor called the machine screw anchor can utilize a setting tool to set the anchor before the screw is inserted. The machine screw anchor must only be used in solid material because the bottom of the hole is required to allow the anchor to set properly. One type of anchor is manufactured as a male type fastener. It is expanded by striking a nail with a hammer and, as the nail goes into the anchor body, it expands against the inside walls of the hole in the masonry.
Types of Lead Anchors
- Hammer Drive – these anchors are manufactured from Zamac 7 and are made from two parts, the anchor body, nail, and are permanently assembled. The head of the anchor body is oversized for excellent bearing surface against the item being fastened. They come in two diameters of 3/16” and 1/4”, and in different lengths to allow different thickness of material to be fastened. The minimum embedment depth in the base material for all lengths of anchors is 1”. They are all packaged 100 pieces per box.
- Machine Screw Anchor – requires the use of a setting tool for expansion and a bolt with national coarse threads. The designated diameter of the anchor is equal to the bolt diameter that is inserted into it. They are available in diameters from 1/4” to 3/4”.
- Lag Shield- made from two pieces that are permanently attached to each other. A screw with lag threads must be used to insure that the anchor is properly expanded. Minimum embedment is equal to the length of the anchor being installed. The diameter of the screw used is equal to the designated diameter of the lag shield being used. Lag shields come in two lengths for each diameter. The short lag shield is for use in hard base material; the long version is for applications where the base material is soft or suspect.
- Single Expansion- works well in dense hard base material; the two pieces are held together by an expansion ring. A threaded bolt with national coarse threads is used to expand the anchor and must be embedded in the base material a minimum distance equal to the length of the anchor being installed. It is manufactured in six diameters from 1/4” to 3/4”, with the designated diameter equal to the bolt diameter inserted into it.
- Double Expansion – perfect for applications where the base material is soft or suspect because the anchor expands along its entire length and provides consistent holding values. Anchor length equals minimum embedment depth. It is available in diameters of 1/4”, 5/16”, 3/8”, 1/2”, 5/8” and 3/4”.
As with any anchoring project, it is important to keep safety in mind and follow instructions carefully.
Always remember to wear safety goggles, handle all tools with extra care and follow all technical specifications.
This article is meant to serve only as a basic explanation of concrete fasteners.
Always refer to manufacturer's instructions or consult a contracting expert during any anchoring project.
Article Written By:
Mike Pistorino, Vice-President Operations
Concrete Fasteners, Inc. has over 40 years of experience selling concrete fasteners. We can ship out one box or a whole pallet of concrete anchors. Our products are of the highest quality... "your satisfaction is guaranteed". We ship all orders the same day the order is received.