PhD® Outdoor Medium Crew Black - Medium. For a sock that has it all, look no further: the PhD® Outdoor Medium Crew offers fit, comfort and durability wrapped together in one smart sock. Featuring Indestructawool⢠technology for ultimate durability in high wear areas, the 4 Degree® elite fit system for a dialed fit and our signature Virtually Seamless⢠toe for extraordinary comfort in any trail shoe. Medium cushioning provides impact protection and ultimate comfort on the trail.