K-36 had a clear plastic sheet to make slip-on fins for stability. Originally a three 18mm cluster. Starting in 1970, you could fly it on the cluster or 24mm mount. The removable mounts were inserted into a short BT-63 tube that butted into a BT-50 to carry the ejection charge forward.

2001 had oversized balsa fins with no slip-on fins of any kind. It had a single 24mm mount.

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I love sanding.