Churn Dash/Monkey Wrench - a nine patch block

The churn dash is a traditional nine patch block.

(See page on how to make your chosen quilt block any size you like.)
To make the churn dash you take your 3x3 grid;

replace the four corner squares with half square triangles

At this point if we stopped it would be a shoo fly block but we go one step further.
Replace the side pieces with half square rectangles.

Traditionally the block is only two colours

Voila.

Here is a video from Jenny Doan for the Churn Dash quilt made from layer cake squares (10" squares), in the quilt shown on the wall the corner triangles are snowballed for a second variation.

This one is from the "pajama quilter"

This video from Jordan Fabrics uses fat quarters (instructions on how to download pattern included in description)

Quilters cache has a page using yardage to make a 12" block here
Chock-A-Block also has instructions here

Variations
The centre square can be replaced with another subunit such as a four patch, nine patch, or pieced block.
e.g with a rail fence in the centre

This video (again from Jenny Doan)  does a churn dash within a churn dash.

Chock-A-Block has instructions on how to make a 8 1/2"  (unfinished) block here

Missouri Star Quilts also did a "triple play" video with a further three variations

Click here to go to the nine patch page