Here is a (probably overly) detailed tutorial on inserting 1/2″ strips into a block. This is the block in question:
First, cut a rectangle of fabric: 4″ x 5.5″. Then cut two strips for the inserts 1″ x 7″. How did I come up with 7″? I just measured the diagonal of the rectangle and rounded up.
Next, mark the center of the short sides of both ends of each strip.
Cut the rectangle across one diagonal (oops, I didn’t take a picture of that!). Take one triangle from that cut and lay it down on your cutting mat. Line up one strip parallel to the long side – making sure the center mark is to the left of the side (or to the right if you cut right handed!). Disclosure: I am left-handed, although I cut with both hands, I typically cut with my left!
Lay your ruler down so it is parallel to the left (or right!) side of the triangle, with the edge of the ruler touching that center mark at the end of the strip. You want to cut off that tiny piece so you have an easy way to line up the strip to the triangle for piecing.
Put the strip RST on top of the rectangle, you should have a nice 1/4″ notch to line up your pieces — stitch! (This is actually a picture taken for the second side, but it shows how the notch is formed!)
Press that seam – I like to press to one side, usually toward the strip. Now, line up the other triangle, place the piece triangle so the strip is parallel to the long edge with the center mark beyond the edge just like we did in the previous step. Trim off that triangle and piece.
Press – again, I like to press to one side, toward the strip. Now on to the next strip. Generally, just repeat the same steps. Cut across the opposite diagonal. Line up the strip. Trim the little dogear. RST and stitch.
To make absolutely sure that the X lines up perfectly, you’ll do a little extra for the second side of the strip. From the back side of the block, mark the stitch lines across the strip and then mark a line 1/4″ from the raw edge. (It’s really light – if you can’t see that let me know and I’ll make it clearer.)
This indicates exactly where the piece needs to be aligned. Stick a pin through one cross and then to the pieced side 1/4″ in from the raw edge. This is where you want the pieces to connect. Repeat with the other cross. Use those two pins to help you get everything lined up then pin the pieces together – I place a pin parallel to the stitch line and remove it once I get to the first intersection. Once the pieces are secured with a pin, remove the two pins that you used to align the pieces.
Stitch. Press. Voila! I know that’s a lot of detail – but after the first block you can start making shortcuts. Why does this work? Because the 1/2″ strip takes up the same amount as the seam allowance, so you aren’t taking anything away from the rectangle. Here is a view from the back that shows that.