Abh mod/Tractor Beam
The Tractor Beam was introduced in 0.4.6RC1. Along with other parts it exploited Impulse with negative and positive numbers.
As of mod version 0.4.6 the tractor beam parts have two separate UI buttons which allow direct control of pushing or pulling mode. If both modes are used at the same time the tractor beam forces will cancel each other out resulting in a holding mode. For a successful hold it is best to manually assign a target on the target object or ship.