What yarn is recommended to use with the 6.5 mm (K-10.5) crochet hook?

It is recommended that "Weight 4 - Medium" and "Weight 5 - Bulky" yarn weights are used with the 6.5 mm (K-10.5) crochet hook size.

What is the comparable UK size of a K-10.5 crochet hook?

The United Kingdom size of 3 is the same as the US crochet hook size of K-10.5.

The metric size of 6.5 mm is the same as the US crochet hook size of K-10.5.

The US size of K-10.5 is the same as the metric crochet hook size of 6.5 mm.

US Name:	K-10.5
UK Name:	3
Metric Name:	6.5 mm
Yarn Weight:	This crochet hook size works well when paired with the following yarn weight(s). Medium Weight #4: Worsted, Afghan or Aran Bulky Weight #5: Chunky, Craft or Rug

These free crochet patterns were all created using various yarn types and brands, but all use the 6.5 mm (K-10.5) sized crochet hook.