Like a lot of tools, you probably won’t use crowfoot wrench extensions on a regular basis, but boy are they good to have when you do need them. Crowfoot wrench extensions are particularly useful in tight spots where you can’t get a socket over the fastener or there is no room to reach it with a ratcheting or regular box end wrench.

Most crowfoot wrench extensions are available in metric and SAE sizes for 3/8- or 1/2-inch drive ratchets. Most are conventional open-end types, but there are flare wrench versions for brake and other types of fittings.

Using a Crowfoot Wrench Extension with a Torque Wrench

Using a crowfoot extension with a regular ratchet is as simple snapping as it on the drive head. But if you’re using a crowfoot with a torque wrench, you can’t do that. You have to know how to orient the crowfoot on the wrench to get an accurate torque reading.

Here’s why: Torque equals force times distance. When using a torque wrench, you apply the force with the handle. The measurement between the center of the wrench handle and the square drive on the head is the distance. Adding a crowfoot extension parallel to the torque wrench increases that distance by adding the measurement from the center of the wrench drive to the center of the crowfoot jaw. If you set the torque wrench to  50 foot-pounds, the actually torque figure you get when the wrench clicks (or hits 50 on the gauge) is wrong.

One way to ensure an accurate torque reading with a crowfoot wrench extension is to orient the crowfoot 90 degrees to the torque wrench handle (see the photos). That will keep the wrench handle-to-head distance unchanged and the amount of torque at the fastener accurate.

Unfortunately, it’s not always possible to get the crowfoot extension on the fastener with a 90-degree orientation. Now you’ll have to use some math to calculate the actual torque applied to the fastener with the crowfoot extension mounted inline with the torque wrench handle. Here’s the basic formula:

Torque Specification x          Length           = Torque Wrench Setting
Length + Crowfoot

Length is the distance between the center of the torque wrench handle and the center of the wrench square drive.

Crowfoot is the distance between the center of the wrench square drive and the center of the crowfoot jaw.

Let’s apply the formula to determine the wrench setting using a 3/8-inch drive torque wrench along with a 3/4-inch SAE crowfoot extension and a torque specification of 60 foot-pounds:

60 Foot-Pounds (spec) x  14.25
14.25 + 1.25

60 Foot-Pounds (spec) x .9677 = 58 Foot-Pounds

You can use the formula when you have to attach the crowfoot 45 degrees to the torque wrench handle by measuring from the center of the handle to the center of the crowfoot jaw to determine the ‘Length + Crowfoot’ dimension.

If you have to mount the crowfoot extension closer to the handle then the crowfoot length must be subtracted instead of added because the overall length of the torque wrench has decreased.

Another thing to keep in mind is a physically larger the crowfoot extension will also change the distance between the square drive and the center of the crowfoot jaws. As a result, there is no true ‘universal’ crowfoot center-to-center dimension.

Using a crowfoot extension with a torque wrench isn’t hard, it just takes some attention so the actual torque applied is correct. Check out the accompanying photos to learn more.

Crowfoot wrench extensions
You can get crowfoot wrench extensions in all sorts of different sizes and layouts in both ½ inch drive and 3/8-inch drive. This is a set of SAE extensions for a 3/8-inch drive ratchet from one of my toolboxes. (Image/Wayne Scraba)
C3 Corvette rear trailing arm mounting bolt
There are some spots where the only way to tighten a fastener is with a crowfoot extension. And if you need to apply torque to a fastener like this trailing arm bolt on a C3 Corvette, a crowfoot is often the only option. (Image/Wayne Scraba)
Crowfoot wrench extension mounted 90-degrees on torque wrench
A crowfoot extension will affect torque calibration by changing the wrench handle-to-drive head length (distance). The exception is when you mount the extension at a 90 degree angle. This will keep the length unchanged and the amount of torque at the fastener accurate . (Image/Wayne Scraba)
Crowfoot wrench extension mounted inline on torque wrench
When you add a crowfoot extension inline to your torque wrench handle, you will effectively change the torque calibration. You’ll have to compensate by using the formula shown in the text. (Image/Wayne Scraba)
Measuring torque wrench length
To determine torque wrench length, measure from the center of the handle to the center of the square drive. Some torque wrenches are marked at the handle center. None of mine are. (Image/Wayne Scraba)
Measuring crowfoot wrench extension length
To determine crowfoot extension length, measure from the center of the square drive on the head of the wrench to the center open end of the extension jaw. (Image/Wayne Scraba)
Crowfoot wrench extension mounted 45 degrees positive on torque wrench
If the crowfoot extension is mounted at a positive 45-degree angle as shown here, measure from the center of the open end jaw to the center of the square drive. (Image/Wayne Scraba)
Crowfoot wrench extension mounted 45 degrees negative on torque wrench
If the crowfoot extension is mounted at a negative 45-degree angle–pointing rearward on the torque wrench–again measure from the center of the open end jaw to the center of the square drive. But you will subtract this dimension in the formula instead of adding it. (Image/Wayne Scraba)
Keywords
torque wrench
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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.