Greetings, all. John Tuttle asked what Delrin is. It's DuPont's
trademarked name for a very durable acetal engineering plastic (no, I
don't work for them!) It sounds as if these "pistons" move slightly in
the tracker bar holes. Delrin would be a logical choice. It would not
wear the way softer plastics would, nor would it cause significant wear
to the tracker bar, because it is "slippery."

When I searched for "Delrin" on the Web, one hit mentioned rollers for
doors, windows and the like, which should give you a good idea how
durable it is.  I suspect that most of the plastic tape transport parts
in a VCR or cassette deck, or a car stereo for that matter, are Delrin
or a similar material.  Also, most of my model railroad rolling stock
truck frames, and the gearboxes and gears of most of my model
locomotives, are made of acetal engineering plastic, whether or not it
is Delrin. In this application, these parts wear as well as metal.

For everything you ever wanted to know about Delrin, try this Web site:

   http://www.dupont.com/enggpolymers/americas/products/delrin.html

Best Regards,

Joel Hoshaw (mjhoshaw@bellatlantic.net.geentroep)