The Book says, “A Shirt Sleeve Placket is usually inserted into a…tailored shirt or jacket sleeve while the sleeve is still flat and before it is sewn into the garment.” This is the type of placket I found the most of around my house, but it takes a few steps to complete.
In addition to the sleeve piece (again, mine here is a crude one I just free cut out for the lesson), you’ll need a top placket piece that has two peaks and is two wide long by twice the desired length of the placket opening. Also an under placket 1.5 inches wide by the length of the desired placket opening
Flip the sleeve so the wrong side is facing up. Take the under placket piece, wrong side facing up, and place it at the right side of the opening, lining up the left edge of the under placket with the right edge of the opening. Stitch the length of the under placket
Press the unsewn side of the under placket, the right side, over 1/4 inch to the wrong side
Sew in place the length of the opening, 1/4 inch in
Flip the sleeve and finished under placket back, exposing the very top of the under placket and the little inverted arrow point/snipped triangle at the top of the opening.
Now it’s time to prepare the top placket
Fold, right sides together, along the length and sew from the inside fold of at the base of the peak, up around the peak itself and then back down to the half way point. The unsewn length needs to be equal to the length of the placket opening.
Clip, turn, push out corners
So now you’ll have that raw edge length down at the bottom. Clip the top of the opened area to the stitch line on the bottom side
Sew in place the length of the placket opening, NOT the length of the entire top placket
Flip to the other side
And press under the remaining raw top placket length 1/4 inch
Pin the top of the placket in place
And do a fun little top stitch around the entire top, reinforcing near the bottom with a little rectangle of topstitch fun
Now, moving the other side of the placket out of the way, sew the top placket to the remaining length of the placket
Add a cuff and call it a sleeve