Test swatches! Same yarn weight, same stitch count, different needle sizes: 2mm, 3mm, 4mm, 5mm and 10mm : r/knitting
Nagina International US Size 6-4mm Dark Rosewood Crafted Single Point Circular Knitting Needles with Brass Capped 26" Nylon Cord | Yarn Accessories & Supplies - Walmart.com
KP Mindful Fixed US 6 (4mm) Circular Needles
14" Single Point Knitting Needles, US 6 (4mm) — Prym Consumer USA Inc.
How to measure your knitting needles without a gauge | Exchanging Fire
Amazon.com: 16 inch US Size 6 /4mm Stainless Steel Circular Knitting Needles Set for Beginners, Round Metal Knitting Needles with Fixed Lace, Circle Needle for Small Knit Projects Socks, Hats, Christmas Stockings