Let's talk about that term 'recommended' or as sometimes presented on yarn labels, 'suggested' in regards to knitting needle sizes.
Recommended needles are the size of knitting needle which commonly achieves a medium tension for that specific yarn weight (you may think of it as yarn thickness).
For example, if I use the recommended needle size as stated on the yarn's label I am likely to get a medium tension knit fabric...if I was to use a smaller needle than the label suggests, my stitches would be smaller and therefore my fabric would be tighter. If I was to use a bigger needle than the label suggests, the stitches formed would be bigger and therefore the finished fabric would be looser.
Here's a swatch to demonstrate: I used the same yarn, recommended needle size 4mm and I am a medium tension knitter, not particularly loose or tight. I used the recommended 4mm knitting needles in the first section and then switched to 6mm needles before switching again to 3.5mm needles. Same knitter, same yarn, same stitch, just different size needles.
This is important to understand so you can appreciate that your needle choice is an integral element in determining the overall feel and purpose of your knitted fabric.
A tighter fabric would be helpful for a stuffed toy, bootie or anything you want to hold some structure. A looser fabric is perfect for drapey scarves, oversized jumpers, slouchy hats.
Bigger needles make bigger stitches, which means you produce more surface area quicker - this is helpful to know if you want to knit something up quickly, like a scarf. As long as you don't mind quite open, loose stitches you could make a big scarf quickly using bigger needles than the yarn recommends. Equally, if you use smaller needles and find the knitting is tight and uncomfortable, consider changing your needles. You will get much easier and consistent results than trying (and I am sorry to say you will fail) to knit looser...more on that on another post to come or watch Lesson 1 of my Beginners Knitting Course.
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