I am doing gague for the 1st time for a knit down one piece sweater. The pattern calls for size 2 for the collar & size 5 for the body. If I change the body needle size to 6, do I also need to go a needle size for the collar?
My short answer is yes. Are you changing the needle size to achieve gauge per the pattern, or are you changing needles size because you like the resulting fabric on the larger needle. Generally, ribbing, is worked on needles two sizes smaller than the body of the work. Sometimes collars are picked up with a smaller needle, then worked on the same size needle as the body. It is helpful to read the entire pattern before casting on, then work the gauge swatch. I buy an extra skein of yarn to make a really big swatch. I use the swatch to measure gauge of course, but also to test buttonholes, decreases, increases and other design elements before I make the garment.
I hope this helps…Happy Knitting!