Len blinked at Bucky for a few moments in utter incomprehension before he just resolved this strange terminology into something like 'top' and 'bottom' and decided to move on from there.

"First of all, you're the one who got curious, which is why you're in this conversation. But to answer your question - James and I trade off," he said finally, because he didn't give a fuck about keeping that a secret from James himself, and he wasn't about to get prissy about it. "We're both control freaks in different ways, so we switch it up. That help?"