Hi Randy,

The head tube itself is neither threaded or threadless, but the fork
and headset you use will be one or the other.

The original plans call for a 1-1/4" dia head tube. This will allow
for a 1" headset. If you want to use a threadless headset, then you'd
get a fork that has no threads on the tube.

Most of the time, you'll find BMX forks with a threaded tube, and made
for a 1" headset.

If you have found a BMX fork that can be used with oversized MTB
headsets, it will likely be intended for use with a threadless
headset. If you want to use a threaded headset you can thread the fork
tube with the proper tool.

In my opinion, there is no advantage to using a threadless headset on
a recumbent bike. The threaded system may be a little heavier, but it
is very secure and easy to adjust.

You can find the BMX forks that you need from Power On Cycling (
http://www.poweroncycling.com ) Sometimes they have very good
specials and you can get 1" threaded BMX forks with brake bosses for
under $20. They also have plenty of threaded and threadless headsets.

Jim