Black Brant ll Fin unit BT-55 for 24mm motors

BT-55 version of the Black Brant ll. This fin unit accepts 24mm motors, and is sized for Series 9 tubing ( ST-9) or T50H ( heavy wall BT-50) as a more robust substitute for standard BT-50 tubing, and has slightly larger centering ring holes for this reason. You have both options. This is intended as a black powder friction fit design in the old Estes style, to take advantage of the new motor options E-9 and E-12 series.