Concrete Drop-In Anchor ~ Concrete Fastening Systems
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Drop-In Anchors

Concrete Drop-In Anchor

Technical Information:

A Drop-In anchor consists of a zinc plated steel tubular expansion shield and a solid, cone-shaped expander plug. The expander plug is case hardened and tempered to prevent galling and binding during expansion. The shield has four equally spaced slots for a portion of its length and the bottom part may be knurled. The shield also has a smooth, flangeless top that allows for either flush or countersunk installation. The bottom lip of the shield is tapered to allow maximum depth and holding power.


Specification GSA FF-325 Group lll, Type 1.


Light to heavy-duty into solid concrete.


  1. Drill a hole in the concrete using a hammer drill and a carbide tipped masonry drill bit conforming to ANSI B94, 12-77, matching the bit size with the outside diameter of the drop-in anchor being used. Make sure the hole depth exceeds the minimum embedment.
  2. Clear the hole of all debris.
  3. Drive the anchor into hole until it is flush with the surface of the concrete.
  4. Using the proper-sized setting tool for the anchor, expand the anchor by inserting the setting tool into the anchor and set with several solid hammer blows. The anchor is set properly when the shoulder of the setting tool is flush with the top of the anchor. To set anchor below surface: Drill the hole deeper than the anchor length. Thread the bolt into the anchor. Hammer the drop-in anchor into the hole until the bolt head is at desired depth. Remove the bolt and set the anchor with the proper-sized setting tool as described above.

Bolt Length:

When the drop-in anchor is set flush with the base material, the minimum bolt length required equals the internal thread length of the anchor, plus the thickness of the material to be fastened, plus the thickness of any washers to be used.

If the anchor is set deeper into the concrete, adjust the length accordingly, by adding the additional depth to the minimum anchor length.

Anchor Spacing:

The forces on a Drop-In Anchor are transferred to the material in which it is installed. If the anchors are installed too close together, it can cause an interaction of the forces, thus reducing the holding power of the anchors. Minimum spacing between anchors and minimum edge distances for the concrete drop-in anchor are as follows:

Anchor Diameter Spacing Between Anchors Minimum Edge Distance
1/4" 3-1/2" 1-3/4"
3/8" 5-11/16" 2-13/16"
1/2" 7" 3-1/2"
5/8" 8-5/16" 4-1/8"
3/4" 10-1/2" 5-1/4"

When vibration or sudden impact are part of the load condition, spacing between anchors should be increased.

Drop-In concrete anchor/fastener - Technical Data:

Anchor Size Overall Length Drill Bit Diameter Internal Thrd. Length Bolt Dia. Pull-Out 3000 psi concrete
1/4" 1" 3/8" 1/2" 1/4" 2,200 lb.
3/8" 1-9/16" 1/2" 5/8" 3/8" 4,400 lb.
1/2" 2" 5/8" 3/4" 1/2" 7,040 lb.
5/8" 2-1/2" 7/8" 7/8" 5/8" 11,880 lb.
3/4" 3-3/18" 1" 1-1/4" 3/4" 12,980 lb.

Values shown are average ultimate values and are offered only as a guide and are not guaranteed. A safety factor of 4:1 or 25% is generally accepted as a safe working load. Reference should be made to applicable codes for the specific working ratio. Critical applications (vibratory loads, overhead installations, etc.) may require a safety factor of as much as 10:1, or more.

Drop-In Anchor Installation Video