Time and again I find students and indeed professional upholsterers using the wooden web strainer incorrectly. We now have a video of how to use this.

This how NOT to use it. This method defeats the object. It relies totally on how tight you can hold the webbing- you might as well use your bare hands.

The following pictures show how to use the webbing strainer (stretcher) correctly

After fixing the webbing to the furthest side of your frame bring the webbing towards you.
Do not cut the webbing to size.

Hold the web strainer with the rounded end upper most and the stepped edge towards the chair frame. Note: It is sometimes helpful to drop the roll (or excess webbing) to the floor at this point.
Pass a loop of the webbing through the hole and catch it with the dowel at the back

Trap the tail of webbing (that part leading to the roll or excess webbing) between the chair frame and the stepped edge. If you are lucky this will rest at a point where you can wedge the stepped edge under the frame or in a groove on the frame which will stop it slipping.

By trapping the webbing between the frame and the web strainer it cannot pull through in either direction allowing you to pull the webbing extremely tight
You may have to adjust the position of the webbing as it passes through the hole to get the right tension.

However, this method can prove to be extremely efficient be careful on items such as drop in seats or small weak chairs that you do not distort the frame

This picture shows how you can use your body to hold the strainer and still keep the tension on the webbing, leaving both hands free to do your work