Why did I used 3M 101 & Tef-Gel on this machine screw?


Over the last 35 years of boating and messing with stainless steel nuts & bolts I've come to know a phenomenon called "thread galling" quite well. Some may not know what this is, even though they may have experienced it.


Thread galling is most prevalent with fasteners made of stainless steel, aluminum, titanium, and other alloys which self-generate an oxide surface film for corrosion protection.


During fastener tightening, as pressure builds between the sliding thread surfaces, protective oxides are flaked, sloughed or perhaps wiped off. These flaked off pieces create an interference or high point and thus seize or lock the nut and bolt together.


This clogging action causes increasing surface adhesion. In the extreme, galling causes seizing or the actual freezing together of the threads. If tightening is continued, the fastener can be twisted off or its threads ripped out.


Some stainless bolt manufacturers actually refer to this phenomenon as "cold welding." Anyone who has seen a bolt and nut seized in this manner understands the nature of this description.


Please use some sort of lubrication for the threads as this is the only way to minimize thread galling.


Galling is a problem that can occur between two un-lubed stainless pieces such as a nut and a bolt. Essentially, as you begin to tighten they bind together never to come apart again. You never know when this will happen it just does.


The last thing I wanted was to "gall" one of the machine screws into the flange as this would require a drill out and re-tap of the trim ring. I could have used Loc-Tite on the threads, to prevent galling, but I know from experience that Tef-Gel or 3M 101 works and it too prevents the bolt from backing out. I used Tef-Gel at the head of the bolt for lubricity for the stainless to stainless mating where the pan head machine screw meets the ports interior flange. This allows a very smooth tightening of the machine screw with no false "grabbing"..


EDIT: With 3M 101 now discontinued I would suggest using Tef-Gel for both the machine screw threads and under the head. I have not found that Tef-Gel has a tendency to loosen over time if properly torqued.