It's a Fixed Offset Sleeve. The new axle also has Fixed Offset Sleeves. On both axles, the Left and Right Sleeves are different. Can furnish numbers if you like. Or if I didn't lose them...
When I called manufacturer help desks, and when I called truck alignment shops, they did not recommend adjustable sleeves. I know you and several others are using them without issues, but they claim the bushings can jar loose in heavier vehicles. And specifically mention RVs. One shop said "If they have them, we replace them."