Robin String Trimmer with Stihl Head
 

I have had my Robin String Trimmer for at least 8 Years but have never been happy with the trimmer head. It was a two line bump head but the line would weld together or not feed correctly. There were time I spent just as much time messing with the bump head as weedeating. I hired someone to weed eat just because I hated the bump head. He uses a stihl Trimmer and he had to add some new line and I saw that it was a double spool and he seemed able to trim the whole property without any hassle. So I purchased a Stihl Autocut 25-2 to see if I could adapt it to my Robin. The Robin shaft is 8mm X 1.25mm (LHT) while the stihl is 10mm X 1MM (LHT). I had three arbors to work with. I purchased a 8mmX1.25 LHT Tap and a 10mmX1mm LHT Die. I used my shopsmith in the horizontal boring position and chucked up one of the abors and used a file to mill the square end round in order to fit in the Autocut head and then the non-threaded part of the arbor I milled it down to close to 10MM to cut the threads with the die. It took me three tries to get it right but the Stihl head fits perfect. The existing threaded section was cut off. I could not locate any adapters that would work for what I wanted to accomplish. Most of the adapters are made to fit the shaft output and then to their own brand of trimmer head.

We sell this head that has 2 or 3 blades on it, and the blades are replacable. On a gas trimmer I bet you could mow down 1" sapplings with the thing. If you ever tire of the line, get the bladed head for it.

If you were a member with one post, I would mark you as spam LOL
That being said. I tried to read this, and got lost.... very fast.... ohsofly seems to know about this though.

places like lowes or homo depot usually sell non brand name universal replacement heads that will fit most name brands
I have never heard of Robin Brand ,but on second thought maybe some old commercial grade but rare nun the less IMO

I realized universal bump heads come with adapters but I wanted to adapt a stihl bump head to my Robin trimmer. Which I was able to do and it fits and looks and runs like a factory install.

Gas Powered Trimmers :: Robin Equipment Power

I understand what you did / hand to do to make it work
BTW unless you got the Stihl head from a Stihl dealer it may not be much better than the one you had because even Stihl has big box quality and dealer grade

I was using the star profile cutter string and it jammed like a mother
Buddy gave me some square profile stuff they use at his work , works much better