Royston Vasey wrote:

"Spehro Pefhany" wrote
Stuff it into a stubby thin-walled open-ended tube ...

... the flat top end OD is fixed at 16mm and wouldn't fit
through.

Do you *any* leeway here? If the flat top end could be 14mm, say, it
would work nicely. The forming bar & die could be tapered & would work
better than the straight ones.

Bob