There are 2 sizes for Sockguy’s socks “S-M” and “L-XL”.
As a reference, I wear “L-XL” since the smaller size feels a bit tight as my feet are 26cm (US8) and shoes 27.5cm (US9.5).
That said, actually I can wear them both sizes since they fit well and elastic enough.
Not only for riding but also good for your daily life as well as room socks in winter time.
There are few types such as “standard”, “Long socks”, “Wool” and the high-end “SGX6” the model “made for even higher performance”. Even if the description doesn’t make sense to you much, actually it fits even better obviously. It gives you a premium fit with the streamlined sole, seamless toe and arch support on instep.
According to their website, it’s better to flip inside out when you wash them to avoid hairballs. Also, for the best result it’s better not to use softener and do dry them with low temperature.