Spaghetti straps can be hard to turn inside out, especially very narrow ones like you find on Asuka’s sundress, or Aya’s from Parasite Eve. Using this simple technique will make it more painless than you ever thought possible!
As I’m sure you could guess, it starts with a rectangle. Fold it in half, iron it flat, and stitch the strap. (If you have a serger, you may want to serge instead of straight stitch this part if your fabric weave and strap width permit it - drive off the edge at the end for a little while and you can use your excess serger chain as the “thread” for the following steps.)
Make absolutely sure to solidly backstitch at both ends. You don’t want it falling apart when you’re half through turning it inside out. Then give the seam allowance a quick haircut to reduce bulk.
Keep in mind that your seam allowance after it’s trimmed must be smaller than your finished spaghetti strap. Eg, if you want 1/2 inch spaghetti straps, make sure your seam allowance is somewhat less than 1/2 inch. (If you make it 1/2 inch exactly it won’t have space to lay flat once flipped inside out.)
Now, if you’re like most people who have ever sewed anything, you probably have one of those hand sewing needle variety packs that always seem to be 20% usable needles, 80% darning needles. Well, today is your lucky day, because those darn useless needles are about to become relevant. Tapestry or darning needles work great for this because they have blunt tips which won’t poke through the fabric as easily and are often the closest viable object in the vicinity of whatever you are sewing. Yarn needles or the singer upholstery repair kit also work well for this.
Basically, you’re looking for something that’s 1) slender and rigid, with a blunt tip 2) you can robustly affix a load-bearing string to and 3) can pass through the width of your intended strap.
Using the largest, bluntest needle you have (whatever that ended up being), thread it with your heaviest duty thread (eg upholstery thread) and double knot it as shown. If you don’t have upholstery thread on hand, or you’re dealing with a very stiff fabric and a very narrow strap, you may want to reinforce it by threading it with two threads instead of one, or finding a very thin cord.
Attach it to the end of your tube with a few stitches. This is going to get yanked on real hard, so make sure it’s deep enough in that it won’t tear out.
Insertion time! If your needle is REALLY blunt, to the point that it has no chance of piercing or catching on your fabric, you can do it business end first. Otherwise, it’s usually better to stick it through butt end first. It won’t get stuck on things as much.
An action shot…sort of. Pull your needle all the way through to the other side of the tube.
Once it’s clear, go to the other end where you made the knot and use your fingers to start pushing the fabric to the inside. It shouldn’t need much, just maybe a half inch or so to get it turning properly. Gently pulling on the needle thread from the other end can sometimes help get it started. Now you can pull your tube of fabric inside out very easily by simply pulling harshly on the needle-thread assembly.
V for Victory! If your spaghetti straps look like they’ve imbibed a little too much vodka sauce, you will want to make an appointment with your iron. Aren’t you glad you didn’t have to turn that inside out by hand?