Bid 4♣ after partner opens 2♦/♥/♠ or 3♦/♥/♠. Bid 4♦ after partner opens 3♣. Asks for the number of key cards in the preempt suit.

The responses to Roman Keycard Blackwood over Preempts, called Weak Roman Keycard Blackwood by Eddie Kantar are:
1st step - 0 keycards in the preempt suit
2nd step - 1 keycard without the Queen
3rd step - 1 keycard with the Queen
4th step - 2 keycards without the Queen
5th step - 2 keycards with the Queen

If the opener shows zero key cards, the responder may ask for the queen by bidding the next suit. The opener’s first step indicates no queen, and the second step shows the queen.