Abstract: An adapter for detachably mounting a drill bit on an extension, is described as having a button-type catch with outwardly diverging flanges, and a separate, split ring of spring steel for exerting a spring biasing force against the button catch. The button catch is seated in a recess which is formed in the split ring. In another embodiment of the invention, the split ring is provided with a protruding finger for initially holding the button catch, so that it can be easily inserted within the bore of the drill bit extension, prior to the final positioning of the adapter within the bore.