Crochet hooks are made of steel, plastic and alloy metals. Each hook is used with a set size of thread unless otherwise stated in the pattern. A pattern should specify a hook size and a tension, so a larger or smaller hook may be required to achieve that tension. If the crocheting is too loose, use a smaller hook, if the crocheting is too tight, use a larger hook. The table below is to be used as a guide only for thread and hook size.
| Thread Size | Hook Size |
| 100 | 0.60mm |
| 80 | 0.60mm |
| 60 | 0.75mm |
| 40 | 1.00mm |
| 20 | 1.25mm |
| 10 | 1.50mm – 1.75mm |
| 3ply | 2.00mm – 2.50mm |
| 4ply | 2.50mm – 3.00mm |
| 8ply | 3.50mm – 4.00mm |