#0014: Tip for reinserting self-tapping screws into plastic housings

What is a “self-tapping” screw?

Whenever one removes screws from a device – especially a mass produced consumer grade device with a plastic housing; then chances are that the screws that were removed were “self-tapping” screws. As the name suggests, these are screws that are designed to cut their thread into the inner diameter of the plastic hole of the device housing that they are inserted into at the factory.

All self tapping screws have a few distinct qualities in common. These include: a relatively deep thread in order to cut into and grip the plastic, and a wide pitch between these threads in order to more effectively slide into the material. Additionally most self tapping screws tend to come to a sharpened point in order to to aid in aligning the screw as it is inserted into the hole.

So what’s the actual tip?

Well, when reinserting a self-tapping screw into it’s plastic receptacle. It is good practice to initially rotate the screw counter-clockwise (loosen) until you feel it pop or click into place. This process aligns the screw with the pre-existing thread, and in doing so means that when the screw is screwed in, it will slide into the already established thread and not cut a new thread over or across the old one. When aligned correctly, the screw should screw into the hole with very little resistance.

Why use this method?

The reason why this is important, is because repeated re-boring of the plastic hole will eventually strip it out of any threading. This is because each time a new thread is cut into the plastics it removes material; which in turn incrementally widens the diameter of the hole in the process. This can continue to the point that it can no longer effectively hold the original screw within it. Avoiding re-tapping the thread every time you reinsert the screw will minimise your damage footprint when repairing/working on the same devices repeatedly. Which is always good.

Video demonstration

Please note: although it may look like I am using force to reinsert the screw, I am not. It’s just the awkward angle and set up that may make it appear that way.

What to do with an already stripped or overlarge hole?

There are a few remedies to take if this advice is coming to late. The quick and dirty solution is to use a larger size self tapping screw that then can cut a new thread into the widened hole. After which one has to then absolutely makes sure to always realign the new larger screw with it’s thread before reinserting it. This is because any further damage to the plastic hole may make it entirely unusable. E.g. a plastic stand-off splitting entirely due to it’s enlarged hole.

The more intensive repair requires filling the hole with something that the original sized screw can then bite into. The most likely materials used here are either hot glue for a “temporary” fix; or melted plastic of the same type as used by the device for a more permanent solution. If you use the melted plastic route: I recommend filling the hole entirely, then drilling a new hole of the correct diameter. Followed by finally using the original self tapping screw to cut a new thread into this virgin material.