Here's a photo of a partially completed Sprite I am assembling, using a Semroc RT-70 ring and laser-cut fins. The rest is old Estes stock, including a parallel-wound BT-30 and an old balsa cone.

The tube I have is 2.75 inches long and the hole is 1.25 inches from the top.

On my original, the hole was 1.25" from the BOTTOM.

You have to excuse the finishing skills (or lack of them). It was the first rocket I ever built.