It is not always necessary to switch to double pointed needles for finishing a hat knit in the round. If you select the right circular needle- one with a flexible cord - you may be able to complete your project with just one needle. This technique requires you to keep an eye on your tension as the opening gets smaller. If you knit too loosely, the fabric will not have the consistency desired for a great finish and you may even have some unsightly holes. If you knit too tightly, there will likely be some puckering at the top. Tension too tight will also lead to difficulty finishing that final round as the yarn resists your efforts to insert the needle. Aim for being gentle and slowing down for this last part of your project.
In my experience this particular technique is best suited for finishing hats and items made with worsted weight higher. The thickness of the yarn as the needle "pops out" during the round prevents gaps between stitches. This may not be the case if you are using a lighter weight yarn or a very delicate yarn. If you decide to go for it with a lighter weight yarn, keep in mind that regularly adjusting your needles will help prevent pulling the fabric as the size of the opening decreases. This need to constantly adjust reduces the time saving element which is one advantage to not switching to double pointed needles. You may opt to switch anyway with that in mind.
Another other point when using a thinner or more delicate yarn is to adjust your tension to be loose a few rounds before the decreases begin. This will allow for a margin of error if the fabric is pulled out of shape as you decrease. These points are for those knitters who are very particular. Often blocking will relieve any draping issues created by uneven stitches or gaps between stitches. If you are very fastidious you probably will stick with using dpns for the end of the rounds anyway!
My final tip for using this technique when there is concern about the fabric you are knitting getting stretched as you decrease is to use natural fiber yarn, especially wool. Wool offers an inherent stretch due to its structure: coiled with a lot of spring. Wool can help your stitches "bounce back" if they get pulled.
Since I started a YouTube channel to share some of the knitting lessons I have acquired over the years this is hands-down my most popular video. So much so that the original has been replaced with an updated version, and there are plans for a third revision using a light-colored yarn for better visibility. Please watch the video and subscribe to my YouTube channel!
Please watch the video and subscribe to my YouTube channel!