The Secret Sleuth No Show Sock in Black from Smartwool. 

Our lowest-cut sock yet, with a "hidden" height. This secret in your shoe is a non-cushioned No Show sock that's perfect for ballet silhouettes and other flat shoes. An internal silicone heel gripper designed to help keep socks in place, a seamless opening made to help prevent pressure points, and a supportive arch brace make these socks the secret weapon that your sock drawer has been missing.

• Sock Height: No Show
• Virtually Seamless toe for enhanced comfort
• Internal gripper at heel to secure sock fit
• Seamless opening reduces pressure points and enhances comfort
• Supportive arch brace
• Made in USA of Imported Yarns: 60% Merino Wool, 38% Nylon, 2% Elastane