used either when (a) a minor suit fit has been found, where a jump to 4 of the minor asks for aces, or (b) when partner's last bid was 3NT, a bid of 4 of the cheapest unbid suit asks for aces - if all suits have been bid, 5C asks for aces. IN response

1 step shows 0/4 aces
2 step show 1 aces
3 steps show 2 aces
4 steps for 3 aces

To ask for kings, asker must repeat the suit used to ask for aces (e.g., if 4D used to ask for Aces, 5D used to ask for kings
Responses are the same, only 1 level higher.