Traditional round tapered buttons, like those found on Gibson® guitars over the last 50 years. Set of 2 with screws.
 
These are slightly smaller than the strap button found on Fenders.
Button diameter: 0.492" (12.50mm)
Button height: 0.347" (8.81mm)
 
A better match on vintage guitars: the Relic Aluminum set has an aged look, perfect for repairing old guitars, when shiny hardware looks out of place.
Felt Washers help to avoid marring your finish, sold separately.