The most common way of installing tubeless valve stems in a wheel or rim without the correct tool is to use a set of needle nose pliers or vice grips. The problem with this method is two fold – it’s easy to marr the threaded finish of the tubeless stem meaning the plastic cap may not thread back on easily. Secondly, it requires a lot of effort to “pull” the valve stem through the tight fitment of the rim valve hole while holding the tool at an angle.
In contrast, the female valve stem fishing tool threads onto the end of the valve stem so no damage can occur to the threads. Also, when you pull on the tool to seat the valve in the rim hole, the pulling force is coming from directly above the valve stem making it much easier to seat the stem into the rim hole.