Stihl's new style fastener

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I think it helps on quicker installation at the factory without cross threading.


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Pretty coarse thread too by the looks of it.

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Definitely look like thread forming screws. Basically no chance of cross threading as the screw forms it's own as it's driven in and they are very resistant to loosening up. They don't cut the threads they form them in the cylinder material and are basically self locking once torqued down.
 
You have to wonder how many times Stihl tested this design. See post #2. I suppose they assumed that every time the screw is used, it's going into a new cylinder and cutting new threads. That's a rather powerful assumption in my book.
It doesn’t cut them, it forms them. Basically mushes the metal around the threads and shank. Once they’re formed the screw works just like any other, it won’t recut new threads once they’re formed
 
It doesn’t cut them, it forms them. Basically mushes the metal around the threads and shank. Once they’re formed the screw works just like any other, it won’t recut new threads once they’re formed
That's good to know. Seems to me that forming is the same as cutting, but I hate to be picky. I have a feeling these will work out OK and I imagine they have been tested to high heaven. Nice to jaw with another 361 owner. It remains my favorite saw even if its carb does flood occasionally.
 
Yes on thread forming taps ( or screws )
I had one in my too box for years. It was a 3/8-32 TPI. For forming fine threads in brass or aluminum. It was the first fluteless taps I’ve ever seen. Looked like a pointy bolt.


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The idea behind the threads on the screw starting back from the point is that the screw will then self-center and tend not to form a cross thread when used again in the same hole where threads have already been cut (formed) before. Power drive tools may have prompted this idea. I personally do not use power drive tools when setting cylinders back inro the case.
 
Using power drives on fasteners , especially in aluminum or magnesium, can get you in trouble pretty quick.
Cross thread, stripped threads, twist bolts or screws off. I just do it the old slow way. And considering you don’t damage anything, it can be faster in the long run.


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They have had that type screw on clamshells for years so they are tried and true. The old ones just had threads all the way to the tip, but were self tapping too.
 
That's good to know. Seems to me that forming is the same as cutting, but I hate to be picky. I have a feeling these will work out OK and I imagine they have been tested to high heaven. Nice to jaw with another 361 owner. It remains my favorite saw even if its carb does flood occasionally.
The big difference is that a cut thread is made by removing material. A formed thread doesn’t remove any material, it just moves it around, in this case the aluminum gets extruded toward the shank of the screw and fills the gap between the threads
 

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