There is a certain “feeling” one gets when using a specific purpose tool, to do what it does best; enter the Fein Multimaster.
Aside from it’s prowess at detail sanding, fitted with the 2.5″ E-Z Cut saw blade, or as I like to call it, “The 1/2 Forrest”, it excels at undercutting door casings when installing flooring materials.

In this small room getting ceramic floor tile, there are but four casings to undercut. Having zipped through the first three, I’m wondering what is hanging-up on the last one. With just a cursory glance, it’s immediately clear what the problem is. There are no teeth left in the center of the blade; some dim wit saw fit to toenail the casing to the sub floor. It was after 6 P.M. so I packed-up for the day.

Mulling over the situation during the drive home, I resigned myself to the fact that I would have to pony-up another $55.00, (thus the moniker “1/2 Forrest”). Fine, but what about the turn-around time, the client wants the room finished.

None of my files are narrow enough to re-shape the tiny, missing teeth. Ah, what have we here, a thread restoring file. I tried the Metric file first, then the fine and finally found a match on the coarse file. The 18 tpi. segment restored the damaged section back into service.
These thread restoring files are .5″ sq. X 8.5″ long, and have 3.25″ of four different TPIs at each end, or eight patterns total, per file. There are three flavors of thread restoring files I know of, SAE coarse, SAE. fine and Metric. Having all three is not a great inve$tment, but they are a definite asset. Although I have all three, I can’t recommend any single one as being the most often used, but having less than the three, the missing one would be the most needed.
Since such a tool has been around for quite a while, there have been others to market it. I give you my brand as a starting point;
Nu-Trix | #1 | USS SAE | 11, 12, 13, 14, 16, 18, 20 and 24 TPI
Nu-Trix | #2 | USS SAE | 9, 10, 12, 16, 20, 27, 28 and 32 TPI
S&G Tool Aid |0.75,1.00,1.25,1.50,1.75,2.00,2.50 and 3.00 Metric

TIP: For restoring the damaged Fein, one cannot use the thread restoring files in the usual manner; instead, secure the file and drag the EZ-Cut cut blade across the stationary file.