Quarter Square Triangle (QST)

You can either design a quilt block while designing a quilt or from the 'BLOCKS' dashboard.
Create a New Block
If you're already working on a quilt, create a new block by:
Click on the 'BLOCKS' tab on the left-side control panel.
Click on the 'Make Custom Block' button.
The Block Editor window will open.
TIP: You can also change the name of your block in the 'Block Info' area.
Input the desired width and height of your block.
Note: These measurements are for the finished size of the quilt block.
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Quarter Square Triangle Block
Change the grid lines to 2 for both horizontal and vertical units.
Click on the isosceles triangle shape. It will appear in the middle of the quilt block.
Move the triangle shape to the lower left corner of the block.
Resize the shape so that it fills the entire width of the block and half of the height of the block. 
TIP: Do this by clicking on the appropriate square around the shape and drag it into the desired position.
Click on the triangle and then click on the 'Clone' button in the center vertical control panel. Now there are two triangles.
Change the color of the new triangle by clicking on the 'Link' button of a different color tag (in this example, I used color tag B (black).
Rotate the triangle by clicking on the 'Rotate' button in the center vertical control panel.
Move the triangle so that it is aligned with another side of the block.
Repeat steps 5-8 two more times so that each side of the block has a triangle.
Click on the top right button to save the block and click on 'Save To Quilt'.
TIP: You can either save the block to the quilt you're working on OR to your block library.
Now your new block is available on the left-side control panel and can be added to your quilt.