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

and a Double Take with two more variations

If you make the block using an uneven 3x3 grid then that gives you the Alaska Homestead block

Click here to go to the nine patch page