A crawler device for pulling a leader string through electrical or cable conduit. The crawler device has a traction head, for example using caterpillar-type rubber tracks, biased outwardly into contact with the inner wall of the conduit when inserted in the conduit. The traction head pulls its own motor...http://www.google.es/patents/US7954575?utm_source=gb-gplus-sharePatente US7954575 - Leader string pull-through machine
