Here are some black, round, plastic, button cord lock stoppers #CL2

They are sold in lots of 2, 6, and 10.

They are round button style, 2 hole.

The hole size is  8 mm =5/16 and is spring loaded

They measure  11/16 =17mm wide and 5/8 =15mm tall
Also have a smaller size see store.

They are used with Drawstring, Paracord, Lanyards, Luggage, Clothing, Hand bags, Backpacks, and Purses.  

Check out other colors and styles - see store under "toggle buttons" or "drawstring cord end stop caps".