Dải đánh dấu cho ống tên lửa 4 inch

Slip this marking band around a 4-inch model rocket tube, and easily mark 3-fin and 4-fin slots, half-way-between lines, other-side-of-the-rocket holes.

The Square indicators show the 4-fin major markings, and the Triangle indicators show the 3-fin major markings. The  minor markings (half-way between 3-fins or 4-fins slots) are not marked, but I'm pretty sure you can find the right ones once you have the major marks on.

I used an Estes PS-II 4-inch tube. Some other manufacturers' tubes have slightly bigger outside diameters, so you might need to scale up just a smidge to fit them.