Developed by Douglas Drury. The player at the 3rd or 4th position may open by bidding 1 major with a relatively weak hand. Responder may ask that the openning is weak or not by bidding 2 Clubs. 2 Diamonds rebid of the opener shows a weak hand and the rebid of the openning suit shows normal strength. The other rebids of the opener are natural. Drury application requires 10-12 points.
Some players use this convention in a reverse way whereas the rebid of the openning suit shows a weak hand and 2 Diamonds shows normal strength. This is called Reverse Drury. This application could be extend that any rebid of the opener other than the rebid of openning suit is natural and shows normal strength.
Bergen Drury is a version of the original convention interpreted by Marty Bergen. In this version, responder asks by bidding 2 Clubs with 3 cards support to the openning suit, asks by bidding 2 Diamonds with 4 cards support. Repeat of the openning suit indicates a weak hand, the other rebids are natural.