Steel Manufacturing Blog: Keeping it Steel

Askew Head Bolts: An Overview of the Variable Considered When Estimating the Size Required

Posted on Mon, Sep 21, 2020 @ 08:37 AM

Askew head bolts are used in masonry work in conjunction with wedge inserts. The askew head bolt is inserted into the wedge insert, which is embedded in a concrete wall, to allow for a connection to be made with a steel member (usually a relieving or lintel angle). 

New construction projects almost always call for an askew head bolt with a bolt diameter of 3/4"; in the past however, many projects used an askew head bolt with a bolt diameter of 5/8". These will often be found in renovation work. When the diameter of an askew head bolt changes, so do the dimensions of the bolt's head. 3/4" diameter askew head bolts have a bolt head that measures 1-1/4" x 1-1/4", while 5/8" diameter askew head bolts have a bolt head that measures 1-1/8" x 1-1/8". This is an important distinction, as both sizes require properly fit wedge inserts to match. An askew head bolt with a 3/4" bolt diameter will not fit in a wedge insert designed for a 5/8" diameter askew head bolt, and vice versa. Figure 1 below shows the difference between a wedge insert designed for a 3/4" diameter askew head bolt and a 5/8" diameter one. The regular and long wedge inserts, which can be found on new construction projects, both use a 3/4" diameter bolt.


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The barrel length (shown in Figure 2 above) is measured from the underside of the head at the mid-point of the slope of the bolt head. The chart on our website shows the lengths available. To estimate the length required, consider the thickness of what it passes through. In order from the inside out, the measurement should start from the face of the wedge insert, to any shims required, to the the steel angle, and finally to the flat washer and the nut. It's critical to ensure that both the new threads are fully engaged.

The most complicated variables to consider when estimating bolt length are the face of the wedge insert and the shim. For instance, the thickness of the wedge insert's face can change depending on where the askew head bolt sits within it. A long wedge insert may have a face thickness of 1/4" to 1/2" depending on where along the slope the askew head bolt sits. Shims are required to provide separation between the concrete and the angle, however variations in the concrete depth will require a different thickness of the shim from location to location. For these reasons, fabricators and erectors will typically request an assortment of bolt lengths and shim thicknesses.

Due to the reality of concrete forming and field conditions, The Steel Supply Company understands there can be considerable difficulty in estimating quantity requirements for askew head bolts and hot dip galvanized slotted steel shims. For those reasons, we stock very deep quantities of all the various lengths of askew bolts as well as hot dip galvanized slotted shims in a wide variety of dimensions.