Sorry for the lengthy URL but I'm after one of these http://cgi.ebay.co.uk/Airpax-digital-linear-actuator-w-shaft-motor_W0QQitemZ250402236743QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a4d22e947&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A4%7C39%3A1%7C72%3A1683%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A200 (http://cgi.ebay.co.uk/Airpax-digital-linear-actuator-w-shaft-motor_W0QQitemZ250402236743QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a4d22e947&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A4%7C39%3A1%7C72%3A1683%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A200)
It's a rotary stepper motor which has been modified to convert the rotary motion to a linear movement, the threaded shaft would need to be about 3-5" long. The one on ebay is a Airpax Model L92211-P1
If anyone has something like this knocking around then I could make very good use of it.
Many thanks
Robert