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Drop-In Anchor FAQ

What is a drop-in anchor?

Purchase Drop-In Anchors

Drop-in anchors are concrete fasteners designed for use in solid concrete only. Once the fastener is set, it becomes permanent.

When should I use one?

If you need to permanently fasten something to concrete (not brick or block), this is a great choice.

How does it work?

The anchor sets in the concrete when the internal expander plug is pushed into the bottom of the anchor with a drop-in anchor setting tool. The plug causes the anchor to expand in the hole and is kept in place by friction.

What materials are used?

These anchors are available in both 304 and 316 stainless steel.

What sizes are available?

They are available in five sizes: 1/4”, 3/8”, 1/2”, 5/8”, and 3/4”.

How many parts does it have?

It consists of two parts: the expander plug and the anchor body. The expander plug and anchor body come preassembled and ready for installation.

How strong is it?

The strength depends on several factors: the size of the anchor, the depth of the hole that the anchor is placed and the strength of the concrete.

What is the difference between a drop-in anchor and a machine screw anchor?

A drop-in anchor is designed for solid concrete, while a machine screw anchor is designed for use in brick, block, and concrete.

Does this anchor come with a bolt?

No, it does not come with a bolt because every application requires different lengths and head styles of bolts.

How do I install a drop-in anchor?

Simply drill the correct size hole, clean the hole, install the anchor, and use a setting tool to set the anchor. For more detailed instructions, visit our Tips & Tricks section.

What size of hole should be drilled?

This anchor requires a masonry bit that is equal to the outside diameter of the anchor.

Why does the hole need to be larger than the anchor size?

The hole drilled is bigger than the anchor diameter because the anchor diameter is equal to the internal or bolt diameter. The diameter of the hole required is the equal to the outside diameter of the anchor.

Do I need to clean out the hole before installation?

Yes. A properly cleaned hole in the concrete is critical.

Do I have to use a setting tool?

Yes, a drop-in setting tool must be for proper installation.

Does installation require epoxy?

No, it does not require any epoxy. Epoxy should not be used.

Can I install the anchor below the surface of the concrete?

Yes. The anchor can be installed below the surface of the concrete, as long as the setting tool is long enough to properly set the anchor. In many applications, embedding the anchor deeper results in better holding values.

How far apart should the anchors be installed into the concrete?

The minimum spacing between anchors in concrete must be equal to ten anchor diameters.

Why do some anchors have bumps on the sides of the anchor?

Some manufacturers make the anchor with ridges on its sides while other manufacturers choose not to add ridges.

What other names are used?

Drop-in anchors are sold under a variety of names, including: drop-in, female anchor, hdi, Hilti drop-in anchor, concrete drop-in anchor, sup-r-drop, HDI anchor, lip drop-in anchor, HDI-L anchor, HDI-P anchor, thunder drop, multi-set, concrete anchor, mini drop-in, and coil thread drop-in

Can I get a drop-in anchor that is made in America?

Yes. Concrete Fasteners, Inc. manufactures anchors in the United States of America under the brand name of Thunderstud.