The New Estes ARF Fin Can

ARF = "Almost Ready to Fly"

Here's the slide - lock fin can on the upcoming Estes ARF models.

We've all seen the "slide the root edge tab in the slot" models before. MPC (now Quest kits and parts CLICK HERE) was the first to use this in the 1970s.
What's looks different here is the locking ring. In addition to retaining the engine it might also prevent the fins from sliding back out the slots.
I haven't seen the 24mm Booster-55 and Booster-60 units up close. CLICK HERE
These new fin cans look to be the 18mm engine equivalent.

Most all the "Coming Soon" BT-55 and BT-60 based ARF models use one of these cans with different shaped fins.